As just confirmed by FOURZEROTWO (community manager Infinity Ward) on the official COD 4 Boards
Alright, heres the deal. The Variety Map Pack is REGION LOCKED. Which means the Region (Language) of the Variety Map Pack, must match the region (Language) that your Call of Duty 4: Modern Warfare disc is.
If you have the GERMAN version of the game, you MUST purchase the GERMAN version of the map pack.
If you have the UK version of the game, you MUST purchase the UK version of the map pack.
Just make sure that the Disc version and the Map Pack version matches up.
If you have any other questions, please let me know.
Apperently some users with the correct region disc still seem to have the same error though, update on that issue to be expected soon.
fourzerotwo : "We're currently talking with Sony to see what option they'll have for PSN customers who purchased the incorrect version. I'll keep you updated on what we hear back."
fourzerotwo added an official statement on his blog