我通过Test over the air这种方式测试iOS程序，但是有时会遇到“无法下载应用程序”的错误，详细信息里只提示“当前无法下载xxx”。
对于这种情况，该如何诊断呢？
以前遇到过这种问题，比如目标平台的要求设定过高（如iOS 5.1但手机只有5.0），或者是简单的网络问题等。
补充：部署到自己的服务器上无法下载和安装，但是通过TestFlight可以，所以目前安装包应该没有问题。我还用iPhone Configuration Utility看了一下手机的控制台输出，似乎也没有看到什么问题，日志如下（Chrome, iPhone 4, iOS 5.1.1, 越狱版）：

''Oct 24 11:01:38 unknown SpringBoard[63] <Notice>: Posting 'com.apple.iokit.hid.displayStatus' notifyState=1
Oct 24 11:01:38 unknown UserEventAgent[19] <Warning>: DEBUG: Changing screen blanked state: 0
Oct 24 11:01:38 unknown SpringBoard[63] <Notice>: MultitouchHID: detection mode: 255->0 (deferring until bootloaded)
Oct 24 11:01:38 unknown SpringBoard[63] <Notice>: MultitouchHID: device bootloaded
Oct 24 11:01:38 unknown SpringBoard[63] <Notice>: MultitouchHID: detection mode: 0->0
Oct 24 11:01:38 unknown kernel[0] <Debug>: set_crc_notification_state 0
Oct 24 11:01:39 unknown calaccessd[2457] <Notice>: MS:Notice: Installing: (null) [calaccessd] (690.10)
Oct 24 11:01:39 unknown sandboxd[2459] <Notice>: MS:Notice: Installing: (null) [sandboxd] (690.10)
Oct 24 11:01:44 unknown kernel[0] <Debug>: launchd[2461] Builtin profile: container (sandbox)
Oct 24 11:01:44 unknown kernel[0] <Debug>: launchd[2461] Container: /private/var/mobile/Applications/92BF7598-F310-431C-A39B-06C532D6B509 [69] (sandbox)
Oct 24 11:01:44 unknown Chrome[2461] <Notice>: MS:Notice: Installing: com.google.chrome.ios [Chrome] (690.10)
Oct 24 11:01:44 unknown Chrome[2461] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Activator.dylib
Oct 24 11:01:44 unknown Chrome[2461] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/SogouInputIPhone4.dylib
Oct 24 11:01:45 unknown Chrome[2461] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/libstatusbar.dylib
Oct 24 11:01:45 unknown Chrome[2461] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/qihoo.360safesrv.dylib
Oct 24 11:01:45 unknown Chrome[2461] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/qihoo.360safesrv1.dylib
Oct 24 11:01:46 unknown lsd[2462] <Notice>: MS:Notice: Installing: (null) [lsd] (690.10)
Oct 24 11:01:48 unknown securityd[2464] <Notice>: MS:Notice: Installing: (null) [securityd] (690.10)
Oct 24 11:01:51 unknown keybagd[2466] <Notice>: MS:Notice: Installing: (null) [keybagd] (690.10)
Oct 24 11:02:04 unknown itunesstored[2468] <Notice>: MS:Notice: Installing: com.apple.itunesstored [itunesstored] (690.10)
Oct 24 11:02:05 unknown wifid[24] <Error>: WiFi:[372740525.352535]: Client itunesstored is background application
Oct 24 11:02:12 unknown sandboxd[2470] <Notice>: MS:Notice: Installing: (null) [sandboxd] (690.10)
Oct 24 11:02:12 unknown SpringBoard[63] <Warning>: could not save thumbnail for downloading icon: image=(null) path='/var/mobile/Library/SpringBoard/DownloadingIconImageCache/com.xyz-68B854CC-8188-490F-B895-041B36C63C06'
Oct 24 11:02:12 unknown installd[2472] <Notice>: MS:Notice: Installing: (null) [installd] (690.10)
Oct 24 11:02:13 unknown installd[2472] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/AppSync.dylib
Oct 24 11:02:13 unknown installd[2472] <Warning>: AppSync loaded into /usr/libexec/installd
Oct 24 11:02:13 unknown SpringBoard[63] <Warning>: could not save thumbnail for downloading icon: image=(null) path='/var/mobile/Library/SpringBoard/DownloadingIconImageCache/com.xyz-77B038CA-2D1D-4985-928C-2A3271FDA412'
Oct 24 11:02:15 unknown SpringBoard[63] <Warning>: Chrome[2461]: Could not stat /private/var/mobile/Applications/92BF7598-F310-431C-A39B-06C532D6B509/tmp/etilqs_Xqc6Sge1rmJT944: No such file or directory
Oct 24 11:02:15 unknown SpringBoard[63] <Warning>: Chrome[2461]: Could not stat /private/var/mobile/Applications/92BF7598-F310-431C-A39B-06C532D6B509/tmp/etilqs_PwcdDzBzGOMgrB8: No such file or directory
Oct 24 11:02:15 unknown SpringBoard[63] <Warning>: Chrome[2461]: Could not stat /private/var/mobile/Applications/92BF7598-F310-431C-A39B-06C532D6B509/tmp/etilqs_cvGlKI57OhTXiVd: No such file or directory
Oct 24 11:03:25 unknown aggregated[62] <Warning>: PLAggregateState Error: Leaving state pluggedin_screen_off even though we are not in it, doing nothing
Oct 24 11:03:25 unknown aggregated[62] <Warning>: PLAggregateState Error: Leaving state pluggedin_charging even though we are not in it, doing nothing
Oct 24 11:03:25 unknown aggregated[62] <Warning>: PLAggregateState Error: Leaving state unplugged_screen_off even though we are not in it, doing nothing
Oct 24 11:03:25 unknown UserEventAgent[19] <Warning>: DEBUG: Changing powered state: 0
Oct 24 11:03:25 unknown kernel[0] <Debug>: AppleD1815PMUPowerSource: AppleUSBCableDetect 0
Oct 24 11:03:25 unknown kernel[0] <Debug>: AppleSynopsysOTGDevice::handleUSBCableDisconnect
Oct 24 11:03:27 unknown aggregated[62] <Warning>: PLAggregateState Error: Leaving state unplugged_asleep even though we are not in it, doing nothing
Oct 24 11:03:27 unknown aggregated[62] <Warning>: PLAggregateState Error: Leaving state unplugged_screen_off even though we are not in it, doing nothing
Oct 24 11:03:27 unknown aggregated[62] <Warning>: PLAggregateState Error: Leaving state pluggedin_screen_off even though we are not in it, doing nothing
Oct 24 11:03:28 unknown UserEventAgent[19] <Warning>: DEBUG: Changing powered state: 1
Oct 24 11:03:28 unknown securityd[2477] <Notice>: MS:Notice: Installing: (null) [securityd] (690.10)
Oct 24 11:03:28 unknown sandboxd[2476] <Notice>: MS:Notice: Installing: (null) [sandboxd] (690.10)
Oct 24 11:03:28 unknown kernel[0] <Debug>: AppleD1815PMUPowerSource: AppleUSBCableDetect 1
Oct 24 11:03:28 unknown kernel[0] <Debug>: AppleD1815PMUPowerSource: AppleUSBCableType USBHost
Oct 24 11:03:28 unknown kernel[0] <Debug>: AppleSynopsysOTGDevice::handleUSBReset
Oct 24 11:03:28 unknown kernel[0] <Debug>: AppleSynopsysOTGDevice::handleUSBReset
Oct 24 11:03:28 unknown kernel[0] <Debug>: launchd[2475] Builtin profile: ptpd (sandbox)
Oct 24 11:03:28 unknown ptpd[2474] <Notice>: MS:Notice: Installing: (null) [ptpd] (690.10)
Oct 24 11:03:28 unknown ptpd[2474] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Activator.dylib
Oct24 11:03:29 unknown ptpd[2474] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/SogouInputIPhone4.dylib
Oct 24 11:03:29 unknown ptpd[2474] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/libstatusbar.dylib
Oct 24 11:03:29 unknown ptpd[2474] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/qihoo.360safesrv.dylib
Oct 24 11:03:29 unknown ptpd[2474] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/qihoo.360safesrv1.dylib
Oct 24 11:03:29 unknown ptpd[2474] <Notice>: PTP interface has been activated at high speed.
Oct 24 11:03:29 unknown kernel[0] <Debug>: launchd[2474] Builtin profile: ptpd (sandbox)
Oct 24 11:03:30 unknown lockdownd[37] <Error>: libMobileGestalt copyMobileEquipmentIdentifier: No MEID in CT mobile equipment info dictionary - <CFBasicHash 0x2564f0 [0x3f967650]>{type = mutable dict, count = 5,
entries =>
1 : <CFString 0x2565a0 [0x3f967650]>{contents = "kCTMobileEquipmentInfoCurrentSubscriberId"} = <CFString 0x2565e0 [0x3f967650]>{contents = "460012300660487"}
2 : <CFString 0x2564a0 [0x3f967650]>{contents = "kCTMobileEquipmentInfoCurrentMobileId"} = <CFString 0x2564d0 [0x3f967650]>{contents = "013130002556488"}
4 : <CFString 0x256620 [0x3f967650]>{contents = "kCTMobileEquipmentInfoICCID"} = <CFString 0x256650 [0x3f967650]>{contents = "89860111608311072596"}
11 : <CFString 0x256670 [0x3f967650]>{contents = "kCTMobileEquipmentInfoIMEI"} = <CFString 0x2564d0 [0x3f967650]>{contents = "013130002556488"}
12 : <CFString 0x2566e0 [0x3f967650]>{contents = "kCTMobileEquipmentInfoIMSI"} = <CFString 0x2565e0 [0x3f967650]>{contents = "460012300660487"}
}
Oct 24 11:03:30 unknown lockdownd[37] <Notice>: 00381000 copy_meid: MobileGestalt failed to provide an MEID but returned no error (?)
Oct 24 11:03:30 unknown installd[2484] <Notice>: MS:Notice: Installing: (null) [installd] (690.10)
Oct 24 11:03:30 unknown installd[2484] <Notice>: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/AppSync.dylib
Oct 24 11:03:30 unknown installd[2484] <Warning>: AppSync loaded into /usr/libexec/installd
Oct 24 11:03:31 unknown mc_mobile_tunnel[2487] <Notice>: (Note ) MC: mc_mobile_tunnel starting.
Oct 24 11:03:31 unknown mc_mobile_tunnel[2487] <Notice>: (Note ) MC: mc_mobile_tunnel shutting down.
Oct 24 11:03:31 unknown mc_mobile_tunnel[2488] <Notice>: (Note ) MC: mc_mobile_tunnel starting.
Oct 24 11:03:31 unknown mc_mobile_tunnel[2488] <Notice>: (Note ) MC: mc_mobile_tunnel shutting down.
Oct 24 11:03:31 unknown lockdownd[37] <Notice>: 00381000 set_response_error: handle_start_session SessionActive
Oct 24 11:03:35 Waynes-iPhone mc_mobile_tunnel[2490] <Notice>: (Note ) MC: mc_mobile_tunnel starting.
Oct 24 11:03:35 Waynes-iPhone mc_mobile_tunnel[2490] <Notice>: (Note ) MC: mc_mobile_tunnel shutting down.
Oct 24 11:03:57 Waynes-iPhone CommCenter[68] <Notice>: No more assertions for PDP context 0.  Returning it back to normal.
Oct 24 11:03:57 Waynes-iPhone CommCenter[68] <Notice>: Scheduling PDP tear down timer for (372740937.446775) (current time == 372740637.446801)
Oct 24 11:03:57 Waynes-iPhone CommCenter[68] <Notice>: Client [com.apple.persistentconnection[apsd,61]] is telling PDP context 0 to go active.''

----------------------------
11月1日补充：现在的情形似乎是通过WIFI可以下载成功，但是3G不行。原以为是ipa文件的mime类型设置不正确，导致下载时无法看到大小（也许是因为服务器用了gzip的缘故）？而因为iPhone会限制3G环境下载大文件，如果无法看到大小，那么下载了一定时间，或者一定大小后还没完成就放弃了。后来将mime改成application/octet-stream用浏览器下载可以看到大小和进度了（WIFI下载也是），但是。。。3G环境下载还是失败。ipa文件大小只有3.5m左右。