I got these from their forum with people having the same issue, try these out and see if it works.
If you're running Vista or 7, run Windows Update and carefully read all of the Optional updates.
I happen to be running Vista, so the update I needed was called:
Update for Windows Vista KB982519
Make sure you read the description and that it says "Install this update to resolve issues with non compatible applications"
Install that update and it should fix the problem. DO NOT install anything else that you don't think you need. You could end up messing up your drivers.
[R]ight click OGPLANET launcher and press properties>compatibility>change to one that works for you mine is windows NT 4.0(service pack 5)