mail 4.5 won't open after updating software mac OS x 10.6.8

After running the software update on my Imac OS X 10.6.8, my mail app 4.5 won't open anymore, the new one 4.6 won't either. I have tried EVERYTHING I have found on the problem, incl downloading and installing the Mac OSX Upd Combo, the SecUpd2012-004 etc. Both mail applications ARE in the applications folder...

I still get the same message: " It (4.5) can't be used on this version of Mac OS x. Try opening the version of Mail located in the Application folder on your computer...."

Please HELP, what can I do?