SQL SERVER – Fix : Error: 4064 – Cannot open user default database. Login failed. Login failed for user
November 4, 2008 by pinaldave

I have received following question nearly 10 times in last week
though emails. Many users have received following error while
connecting to the database. This error happens when database is
dropped for which is default for some of the database user. When
user try to login and their default database is dropped following
error shows up.

Cannot open user default database. Login failed.
Login failed for user ‘UserName’. (Microsoft SQL Server, Error:
4064)

The fix for this problem is very simple.

Fix/Workaround/Solution:

First click on Option>> Button of
“Connect to Server” Prompt.

Now change the connect to database to any existing database on
your server like master or msdb.

Now click on connect and it will successfully log you in. Once
you login in the system run following statement for your username
and it should fix your problem. Make sure to replace [test] with
your username and master with yourdatabase name.

ALTER LOGIN [test] WITH DEFAULT_DATABASE = master GO

本文来自CSDN博客:http://blog.csdn.net/JimFire/archive/2009/12/29/5096633.aspx

Reference Web URL:http://www.microsoft.com/products/ee/transform.aspx?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=4064