19 September 2011 by Web Bureau
I have been recently getting driven round the bend when setting up SQL Server 2008 R2 on a server which already had a version of SQL 2003.
No matter what we tried it kept returning Error 18456, we had at first thought this was caused by the permissions of the login user we created.
Upon further investigation we realised that the error was occuring before it authenticated the login and actually was unable to connect to the server.
The reason for this is a conflict in the default port 1433 which is being used by by both installations of SQL, to coorect this error we need to change the port that the new version of SQL is listening on.
The details of this are listed below:
Hope fully this will be your problem resolved, remember and add the Login under the security tab if you want to allow for windows authentication.