Might be easier said than done, but remove the zip file that you installed, as well as all the information that is linked to this mod (if you really want, create a new folder somewhere completely different to store the mod, in case you still want to keep it). Just have a run through your Program Files for SA:MP and check what's there/not there. I don't have a copy of SA:MP to tell you exactly what you should have, but others on the forums should.
Make sure you track back the installation of that mod and/or zip file. If you downloaded GTA:SA through a torrent (for example), it can be an issue when you download other external files and try adding it to the game files.
See if those steps are at all effective, if not, you might have to go with the old re-install method.