I was just having the same problem (I think) and I seem to have solved it;
After dropping out a few times and finally the whole client just crashing I went to check the Fonline.txt to see what had gone wrong, but when I tried to open it I was told I coulnt because the file was being used by another process... so I started the task manager and sure enough, there was a (second?) instance of the Fonline.exe running for some reason, so I ended that and now everything seems to be running fine (having said that, this only just happened and we'll see how extended play works out for me).
I suppose chances are if you have rebooted your computer you aren't having this problem anymore, but if it reers up again just have a look at your processes and make sure you dont have a second instance of the fonline.exe running.
Hope that helps!