This one always catches me out, about time I logged it so I don’t need to googlise it everytime!
SQL SERVER – Fix : Error: 18452 Login failed for user ‘(null)’. The user is not associated with a trusted SQL Server connection.
April 14, 2007 by pinaldave
Some errors never got old. I have seen many new DBA or Developers struggling with this errors.
Error: 18452 Login failed for user ‘(null)’. The user is not associated with a trusted SQL Server connection.
Change the Authentication Mode of the SQL server from “Windows Authentication Mode (Windows Authentication)”
to “Mixed Mode (Windows Authentication and SQL Server Authentication)”.
Run following script in SQL Analyzer to change the authentication
ALTER LOGIN sa ENABLE
ALTER LOGIN sa WITH PASSWORD = ”
Taken from SQLAuthority.com