If you are receiving this version mismatch error upon logging in or joining games after today's patch you MUST re-download and reinstall the client. What this probably means is that you are using the old version of the setup file which is not supported by the patching system at this time.

The newest setup file can be found here:
http://signup.leagueoflegends.com/download

Specific instructions for reinstalling

If that solution does not solve your problem with updating, I'm going to redirect you to the following thread for more information:
http://leagueoflegends.com/board/showthread.php?t=27103

i dont have option to uninstall... any suggestions?

Unfortunately if you have the old patcher, there are no other options at this time.

Anyone else having this problem but is certain they have a new version of the setup file (a 500 MB setup file) please post your patcher logs.

Hey, my launcher says retrieving version information.
I must redownload the game?

just install the game once you finish downloading and it auto uninstalls.

WHy are there always poroblems with Lol :S this aptch si not even workign plus i have to redownload 00 lame kinda just wodnering

Reinstalled the game...

now i get the error:
"Unable to connect to the network, pleasy try again later"