Let's SQL Together!
You should be carefull when apllying changes to the producion system. This is especially true for applying Service Packs. The main steps before patching SQL Server are:
If you dont followi the steps it is not necesary to have a problem. But statistically it happens at some time.
Like in this case, when I am shaing my experience in applying SP2 of SQL Server 2008 R2: http://maginaumova.com/master-database-error-after-applying-sql-server-2008-r2-sp2/
Good luck and thanks for reading! :-)