php - 提取form值查询mysql后分页第一页正常第二页出错了是什么问题？

<select name="fname">
<?php 
    $resultTable = mysql_query("SHOW TABLES");
    while($row = mysql_fetch_array($resultTable)){
        echo "<option value=$row[0]>".$row[0]."</option>";
</select>
}

<?php 
    $name = $_REQUEST['fname'];
    $length=3;  
    $pagenum=@$_GET['page']?$_GET['page']:1;  
    $sqltot="select count(*) from $name";  
    $arrtot=mysql_fetch_row(mysql_query($sqltot));  
    $pagetot=ceil($arrtot[0]/$length);  
    if($pagenum>=$pagetot){  
        $pagenum=$pagetot;  
    }  
    $offset=($pagenum-1)*$length;  

    $sql = "SELECT * FROM $name LIMIT {$offset},{$length}";
    $result = mysql_query($sql); 
    echo "<table width='700px' border='1px'>";  
    while($row=mysql_fetch_assoc($result)){
        echo "<tr>";  
        echo "<td>{$row['num1']}</td>";  
        echo "<td>{$row['num2']}</td>";  
        echo "<td>{$row['num3']}</td>";  
        echo "</tr>"; 
    }
    echo "</table>";
    $prevpage=$pagenum-1;  
    $nextpage=$pagenum+1;
    echo "<h2><a href='showdata.php?page={$prevpage}'>上一页</a><a href='showdata.php?page={$nextpage}'>下一页</a></h2>"; 
    mysql_close($conn); 

?>

第一页还能正确的分页并显示数据，一按下一页就出错了：

Warning: mysql_fetch_row() expects parameter 1 to be resource, boolean given in D:ServerWebshowdata.php on line 57

Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in D:ServerWebshowdata.php on line 67

这是怎么回事啊？？？
麻烦各位大神看看~谢谢！