We have recently moved to a new hosting provider which might influence the registration process. The solution is to download the most recent versions of Flame Painter:
Flame Painter 2 - download Flame Painter 2.5.6s version
Flame Painter 3 - download Flame Painter 3.3.1s version
All minor Flame Painter 4 updates should work without issues.
If you are still getting the error message during registration even after updating to the latest version, please email us at support [at] escapemotions.com.