Error "Value cannot be null"

hi all,

I connected to database from Tools->Connect To Databse.

also i used LinqToClasses(DataClasses1.dbml).

For some reason,I deleted database from Server Explorer.And then Connect again To Databse from Tools menu.

But when I Start the project Show Error:

An unhandled exception of type 'system.ArgumentNullException' occurred in system.Data.Linq.dll

Additional Information:Value cannot be null

This error from this code of DataClasses1.Designer.cs :

public DataBaseClassesDataContext(string connection) :

base(connection, mappingSource)

{

OnCreated();

}

please help me....