I have a friend with the same bug of you :
-He uses the maniaplanet.exe
-Create an account and use a Beta key.
-Do 2 or 3 updates auto (Maniaplanet 2 , and a shootmania update).
-he succed to join a server and play in.

Did you have the updates?

Execute the maniaplanet.exe as administrator . Save it in his properties, and set the lowest graphics too .

Try to use Maniaplanet.exe . Do not use Maniaplanetlaucher.exe.

Try to use Maniaplanet.exe . Do not use Maniaplanetlaucher.exe.