Yes i tried to run client directly from the game folder, as an administrator, anyway it doesn't really matter. Also, there is no way to set up game installation path incorrectly, because client will send you an error message. I tried different game distributives, installation folders, compatibilities and so on - no success. I give up untill new version of LU comes out...

Everything is correct, i installed the game and multiplayer on 2 PCs (at work and at home), and both of them are using Windows 7 Ultimate (x86 at work and x64 at home). All settings, paths etc are same and they are quiet easy to setup for me, because i used to play many different GTA multiplayers. Both OS are fresh, with clean games installed. Waiting for hotfix, too bad some people are having same problem and can't play LU, it needs more players online! 

I tried everything from this forum and google, even with different game distributives - still nothing, but everything works perfect with same x86 OS.

Did you try running the client as Administrator?

I tried all launching variants and all compatibilities as i already mentioned above. Installed all MS Visual C++, Net Framework etc, disabled antivirus, still nothing helps. And i noticed many people are having same problem.

That's strange, because i just installed fresh clean OS. Maybe some of system components are missing, who knows.

Same problem, we need client working on x64 OS. Nothing helps... 

I tried about 10 different versions of the game, but the client launches singleplayer after i try to join any server using Windows 7 Ultimate x64. But everything works fine on the same x86 OS. Any chance to see this multiplayer client working on x64 OS? Tried all advices from this forum - nothing helped.