MSSQL Troubleshooting

If the Noodle log contains something like this:

2012.01.24 13:48:51: .intranet,ALERT: ConnectionAllocator: failed to allocate a new connection
2012.01.24 13:48:51: .intranet,ALERT+ The connection pool is empty!
2012.01.24 13:48:51: .intranet,ALERT+ due tocom.inet.tds.ab: Msg 4064, Level 11, State 1, Line 1, Sqlstate 01000
2012.01.24 13:48:51: .intranet,ALERT+ [WIN-5A73M1LPPMU]Cannot open user default database. Login failed.Error code: 4064
2012.01.24 13:48:51: .intranet,ALERT+ SQLState: 01000

Unlisted codes:

01 ambiguous
02 Invalid userid
05 Invalid userid
06 Attempt to use a Windows login name with SQL Authentication
07 Login disabled and password mismatch
08 Password mismatch or password policy clash
09 Invalid password
11 Valid login but server access failure
12 Valid login but server access failure
13 SQL Server service paused
16 user does not have permissions to log into the target database
18 Change password required
27 could not determine the initial database for the session.
4064 Cannot open user default database. Login failed. (wait a few more seconds for the database to start and use net start in the intranet.bat)
18456 can be caused by a firewall

SQL to list all error codes for your MSSQL version:

SELECT error,description FROM sysmessages where msglangid='1033' order by error;