[InvalidOperationException: 超时时间已到。超时时间已到，但是尚未从池中获取连接。出现这种情况可能是因为所有池连接均在使用，并且达到了最大池大小。]
   System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) +1282933
   System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) +105
   System.Data.SqlClient.SqlConnection.Open() +111
   SYEXAM.SQLServerDAL.SQLHelper.ExecuteReader(String query, SqlParameter[] parameters) in E:\C＃程序\SYEXAM\SYEXAM.SQLServerDAL\SQLHelper.cs:229
   SYEXAM.SQLServerDAL.UserDAL.GetUser(String _UserName, String _IDCard) in E:\C＃程序\SYEXAM\SYEXAM.SQLServerDAL\UserDAL.cs:42
   SYEXAM.BLL.UserBLL.ChkLogin(String _userName, String _IDCard, String _PassWord) in E:\C＃程序\SYEXAM\SYEXAM.BLL\User\UserBLL.cs:625
   SYEXAM.Webs.LoginBar.btnLogin_Click(Object sender, EventArgs e) +402
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +105
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +107
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +7
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +11
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +177
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1746