ACE Mega Codec Pack 6.03 Quicktime problems

I installed my self the ace mega codec pack 6.03. I installed the professional version i think. and ever since my quicktime does’t even open. when ever i try and run a quicktime movie on my web browser (firefox) it says “illegal operation, browser has to close”. I tried uninstalling ace codec pack but no good, i believe it may have done something to the registry. i was considering reformatting the computer. but yeah... any help would be great thanks!