I SOLVED this doing the following (this SOLUTION might or not work in your particular case):
since i had this problem ONLY when selecting NA server this is what i did:
1.-start lol.launcher.admin.exe (might work with the regular one but i didnt try that)
2.-selected another server (different from the one you ar having problems with) and let it patch everything,
3.-close it (be sure to close everything LOL related from task manager too)
4.- rename "C:\Riot Games\League of Legends\RADS\projects\lol_air_client_config_na" folder
to "C:\Riot Games\League of Legends\RADS\projects\_lol_air_client_config_na"
(notice an underscore at begining of foldername "_lol_air_client_config_na") i did this to keep it as backup just in case (you can delete it after and if it works)
5.-open lol_admin (again be sure theres nothing related to LOL or RIOT from task manager)
6.- select NA server (or the one you where having problems with)
7.- let it patch (it was a really small under 2 mins patch in my case since i had updated with no problems some days ago), this will redownload/recreate the renamed "lol_air_client_config_na" folder for you again, (thats were the problem was in my case)
8 that was it, i was able to play again
9 (optional) close everything,
10 open regular client, and thats it
i noticed in the fixed folder i had
C:\Riot Games\League of Legends\RADS\projects\lol_air_client_config_na\rel eases\0.0.0.39
and in the backup i had
C:\Riot Games\League of Legends\RADS\projects\lol_air_client_config_na\rel eases\0.0.0.38
and a previous one that cant remember one, also in the fixed folder i had
C:\Riot Games\League of Legends\RADS\projects\lol_air_client_config_na\man agedfiles
and in the original i didnt have this managed files thing.
I hope this works for you, was driving me crazy since i didnt want to redownload everything and i dont have accounts in other servers.