Well yes iff you havent try reinstalling GTA yet i would try it dont worry about saved games, those wont get deleted and iff your worried about losing downloaded cars well you have to, or back them up for single player games , and beta testers are found by the MTA team, u cant apply for it.
(basicly what he said was: i had 1.1 about 4 times , and then wanted to try 1.0 for experimeniting and then tried 1.1 again but didnt work, even reinstalling mta wont help,it did work but isnt anymore , do i have to reinstall GTa completly?and how can i "apply" to become an mta beta tester?