You were banned by a plugin that checks to see if your game is returning PB screenshots as it should. Your game stopped sending them for some reason. If I had to guess, I would say that you may have been lagging a bit and packet loss can result in the screenshots failing.
I do not see anything to suggest that you have been cheating so I have removed the ban. Sorry for the inconvenience and thank you for playing on our server. If you have any further issues with this please post back here and I will try to help you.