rose_eyes

We have recently started our own server with Hexxit however upon logging in we get the back lines as shown below. They seem to be covering everything in the game but as soon as we walk up to them they disappear. I have done quite a thorough search but have had no joy in figuring out what they are or how to get rid of it or turn it off. I have tired pressing F9 as suggested but no joy. Any help or suggestions would be much appreciated! Kind regards, Mrs. rose_eyes and Mr. darren_princ.