Well, it is time that Ubisoft sorted itself out. Anybody can make mistakes. Anybody can provide solutions, but...

I was told the best thing to do is reinstall - I did
Then add the 1st patch again - I did
Thten the second patch - I did
and finally ( well almost) - the 3rd patch
All the patches I downloaded. It didn'r work (there was that ACRSP.EXE error again)
The on suggestion I downloaded the Russian version. It didn't work except the error messages were in Russian.

I would love Ubisoft to get the meassage: Your reputation on handling major problems is going down the tube around the world. Nobody wants to buy a game that you have to reinstall every time there is a patch. Who the hell is going to be interested in AC3!

Get your act together quickly. Let your public know that there is a problem. Apologise and tell them to wait until you have repaired it.