Login Failed for user' (null) '. Reason: not associated with a trusted SQL Server connect

Recently compiled Asp.net in vs2008ProgramWhen connecting to the database, the following error occurs:

Login Failed for user' (null) '. Reason: not associated with a trusted SQL server connection.

 

My connection string is: conn. connectionstring = "Server = pc-201007021400 \ WinCC; uid =; Pwd =; database =" & filename

It seems that uid has an error, and then changed to: conn. connectionstring = "Server = pc-201007021400 \ WinCC; uid = sa; Pwd = 123456; database =" & filename

SA and 123456 are set in SQL Server, so that they can connect to the database normally.