This is an error that I've seen lots of people have, and I also had it and I understand how truly frustrating it is, I'm not sure what causes the error, but I do know how to fix it. Also, sorry in advance if someone else has covered this, but I couldn't find anywhere =P
The Error -
The error occures when someone trys to login, not start up the launcher, simply login. It then appears with an error message, however even with the English patch it doesn't appear to have any part of it English.
Here is a picture of it -

The Fix -
Right click the dbo launcher and run as administrator. The client should now start patching and updating everything ect. Now once this is all done, and the start button allows you to play, DONT 'Start', close it and exit the launcher, now the dbo launcher again as administrator and it should work :)
I just want to state, I never made this fix, I had this error a long time ago and discovered the fix on a website, however I can't remember which.
Will add pictures if anyone wants me too :)