<p>When I executed the following code, I encountered the above error -</p> <pre class="brush:php;toolbar:false;">MySqlConnection mysqlConn=new MySqlConnection("server=127.0.0.1;uid=pankaj;port=3306;pwd=master;database=patholabs;"); mysqlConn.Open();</pre> <p>I tried setting the server to localhost and the user to root, but I got the following error -</p> <pre class="brush:php;toolbar:false;">Error: 0: Unable to connect to any of the MySQL hosts specified. System.Transactions Critical: 0 : <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Critical"><TraceIdentifier>http://msdn.microsoft. com/TraceCodes/System/ActivityTracing/2004/07/Reliability/Exception/Unhandled</TraceIdentifier><Description>Unhandled Exception</Description><AppDomain>DBSync.exe</AppDomain><Exception>< ;ExceptionType>MySql.Data.MySqlClient.MySqlException, MySql.Data, Version=6.7.4.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d</ExceptionType><Message>Unable to connect to any of the specified MySQL hosts.</Message><StackTrace> at MySql.Data.MySqlClient.NativeDriver.Open() at MySql.Data.MySqlClient.Driver.Open() at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings) at MySql.Data.MySqlClient.MySqlPool.CreateNewPooledConnection() at MySql.Data.MySqlClient.MySqlPool.GetPooledConnection() at MySql.Data.MySqlClient.MySqlPool.TryToGetDriver() at MySql.Data.MySqlClient.MySqlPool.GetConnection() at MySql.Data.MySqlClient.MySqlConnection.Open() at DBSync.MainForm.BtnCalculateClick(Object sender, EventArgs e) in c:Documents and SettingsTest01My DocumentsSharpDevelop ProjectsDBSyncDBSyncMainForm.cs:line 51 at System.Windows.Forms.Control.OnClick(EventArgs e) at System.Windows.Forms.Button.OnClick(EventArgs e) at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent) at System.Windows.Forms.Control.WmMouseUp(Message&amp;amp; m, MouseButtons button, Int32 clicks) at System.Windows.Forms.Control.WndProc(Message&amp;amp; m) at System.Windows.Forms.ButtonBase.WndProc(Message&amp;amp; m) at System.Windows.Forms.Button.WndProc(Message&amp;amp; m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message&amp;amp; m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message&amp;amp; m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG&amp;amp; msg) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.Run(Form mainForm) at DBSync.Program.Main(String[] args) in c:Documents and SettingsTest01My DocumentsSharpDevelop ProjectsDBSyncDBSyncProgram.cs:line 27</StackTrace><ExceptionString>MySql.Data.MySqlClient.MySqlException (0x80004005): 无法连接到指定的任何MySQL主机。at MySql.Data.MySqlClient.NativeDriver.Open() at MySql.Data.MySqlClient.Driver.Open() at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings) at MySql.Data.MySqlClient.MySqlPool.CreateNewPooledConnection() at MySql.Data.MySqlClient.MySqlPool.GetPooledConnection() at MySql.Data.MySqlClient.MySqlPool.TryToGetDriver() at MySql.Data.MySqlClient.MySqlPool.GetConnection() at MySql.Data.MySqlClient.MySqlConnection.Open() at DBSync.MainForm.BtnCalculateClick(Object sender, EventArgs e) in c:Documents and SettingsTest01My DocumentsSharpDevelop ProjectsDBSyncDBSyncMainForm.cs:line 51 at System.Windows.Forms.Control.OnClick(EventArgs e) at System.Windows.Forms.Button.OnClick(EventArgs e) at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent) at System.Windows.Forms.Control.WmMouseUp(Message&amp;amp; m, MouseButtons button, Int32 clicks) at System.Windows.Forms.Control.WndProc(Message&amp;amp; m) at System.Windows.Forms.ButtonBase.WndProc(Message&amp;amp; m) at System.Windows.Forms.Button.WndProc(Message&amp;amp; m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message&amp;amp; m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message&amp;amp; m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG&amp;amp; msg) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.Run(Form mainForm) at DBSync.Program.Main(String[] args) in c:Documents and SettingsTest01My DocumentsSharpDevelop ProjectsDBSyncDBSyncProgram.cs:line 27</ExceptionString><DataItems><Data><Key>Server Error Code</Key><Value>1042</Value></Data></DataItems></Exception></TraceRecord></pre> <p>我可以通过mysql workbench连接到mysql服务器并查询数据库。只有代码不起作用。 编辑：我注意到当我使用sharpdevelop时出现错误，而在使用Visual Studio时没有出现错误。</p>