There's a problem for some players like us that get this error, I've been told that they're trying to fix it, some players reported that the problem was solved without any fixes, try to login from now and then and see if the problem keeps on going, if it does just keep this post updated and wait until someone from TW responds, I suggest adding the log file to this post -- search it on your computer :
C:\ProgramData\Mount and Blade II Bannerlord\logs\rgl_log_xxxxx.txt