After installing this (just bought it yesterday) my game reverted to FREE. I still had all files but could not build games.
I uninstalled and installed everything anew and it was always after installing MP5 that weird thing happened.
One thing thats suspicious, is that there was no screen to type my serial number as with the other packs and maybe that caused it.
A search on the board didnt turn up something similar but maybe it happened to someone else too who found a way to work it out.
In case you find my grammar and spelling weird ---> native German speaker ^^