Try substituting the lines to this:

fullscreen=false
windowresolution=1600x900
output=OpenGL

You can change the 1600x900 part for something closer to your monitor's resolution, but not the native one (f.e. if your monitor is 1266x768, change the config file value to 1280x720).
It should work, but in case it doesn't, create a support ticket, making sure you mentioned and linked this forum post in it.

Anyway, let me know if it worked or you proceeded with the ticket after checking ;)