Status 16 means this is record for an alias. 

'\test' is not username, it means this alias for login 'test'.

This login is aliased to the userid, specified in altuid column.

To drop...

Eric, you may want to check MAXDOP query hint.

But to use it you need to re-write all your batch queries.

Igor

From Google:

http://www.extremeexperts.com/sql/articles/ListDBCCCommands.aspx 

There are approximately 130 of  them

Igor

I think correct answer should be :

EXEC sp_change_users_login 'Update_One', 'webuser', 'webuser'