一个button控件

 代码如下

private void button1_Click(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection("Data Source=.\\sqlexpress;Initial Catalog=MySchool;Uid=sa;pwd=sasa;");
conn.Open();
MessageBox.Show("链接打开");

conn.Dispose();//告诉垃圾回收可以回收资源，关闭了链接，清空链接字符串。
MessageBox.Show("dispose");
conn.Open();
MessageBox.Show("链接打开");
}

错误详细信息如下

未处理 System.Data.SqlClient.SqlException
Message=用户 'sa' 登录失败。
Source=.Net SqlClient Data Provider
ErrorCode=-2146232060
class="14"
LineNumber=65536
Number=18456
Procedure=""
Server=.\sqlexpress
State=1
StackTrace:
在 System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
在 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()
在 System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
在 System.Data.SqlClient.SqlInternalConnectionTds.CompleteLogin(Boolean enlistOK)
在 System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, SqlConnection owningObject)
在 System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(ServerInfo serverInfo, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject, SqlConnectionString connectionOptions, TimeoutTimer timeout)
在 System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, TimeoutTimer timeout, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance)
在 System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance)
在 System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection)
在 System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection, DbConnectionPool pool, DbConnectionOptions options)
在 System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject)
在 System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject)
在 System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)
在 System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
在 System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
在 System.Data.SqlClient.SqlConnection.Open()
在 ado.net.Form1.button1_Click(Object sender, EventArgs e) 位置 D:\TDDOWNLOAD\精品就业11年4月\ado.net\ado.net\Form1.cs:行号 23
在 System.Windows.Forms.Control.OnClick(EventArgs e)
在 System.Windows.Forms.Button.OnClick(EventArgs e)
在 System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
在 System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
在 System.Windows.Forms.Control.WndProc(Message& m)
在 System.Windows.Forms.ButtonBase.WndProc(Message& m)
在 System.Windows.Forms.Button.WndProc(Message& m)
在 System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
在 System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
在 System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
在 System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
在 System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
在 System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
在 System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
在 System.Windows.Forms.Application.Run(Form mainForm)
在 ado.net.Program.Main() 位置 D:\TDDOWNLOAD\精品就业11年4月\ado.net\ado.net\Program.cs:行号 18
在 System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
在 System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
在 Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
在 System.Threading.ThreadHelper.ThreadStart_Context(Object state)
在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
在 System.Threading.ThreadHelper.ThreadStart()
InnerException: