I found this error message when i restore the database using the GUI and it appear this error message "Error 3154: The backup set holds a backup of a database other than the existing database"
It because of trying to restore database on an existing active database.
Solution:
RESTORE DATABASE DatabaseName
FROM DISK = 'C:\myDatabase.bak'
WITH REPLACE
Use WITH REPLACE when using RESTORE command when u saw above error message "Error 3154: The backup set holds a backup of a database other than the existing database"
Tested in MSSQL 2005
