1. Using SQL Server Authentication
    USE SpiraTeam
    GO
    EXEC sp_change_users_login 'Update_One', 'SpiraTeam', 'SpiraTeam'
    GO
  2. Using Windows Authentication on Windows 2003/2008/Vista/7
    USE SpiraTeam
    GO
    ALTER USER SpiraTeam WITH LOGIN = [NT AUTHORITY\NETWORK SERVICE]
    GO
  3. Using Windows Authentication on Windows XP
    USE SpiraTeam
    GO
    ALTER USER SpiraTeam WITH LOGIN = [MACHINENAME\ASPNET]
    GO

The example above was written with SpiraTeam in mind, since it uses the database name 'SpiraTeam'. If you are experiencing the same issue with SpiraTest, SpiraPlan or KronoDesk, please substitute the name in the SQL commands accordingly.