Server Error in '/' Application.

The ConnectionString property has not been initialized.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: The ConnectionString property has not been initialized.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[InvalidOperationException: The ConnectionString property has not been initialized.]
   System.Data.SqlClient.SqlConnection.PermissionDemand() +7122241
   System.Data.SqlClient.SqlConnectionFactory.PermissionDemand(DbConnection outerConnection) +32
   System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions) +315
   System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry) +128
   System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +265
   System.Data.SqlClient.SqlConnection.Open() +133
   MathExpress.DataAccess.ThuVienDAOTableAdapters.ThuVien_BaiToanTableAdapter.CountByActive() in D:\2023\HTN\Src\MathExpress\DataAccess\ThuVienDAO.Designer.cs:16593
   ME_ThuVien_ThuVien_Main.LoadData() +808
   ME_ThuVien_ThuVien_Main.Page_Load(Object sender, EventArgs e) +190
   System.Web.UI.Control.OnLoad(EventArgs e) +108
   System.Web.UI.Control.LoadRecursive() +90
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1533


Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.8.4110.0