Board Thread:Bug Reports/@comment-27689279-20151227021542/@comment-25612015-20160105061302

Illegal extra prefix errors are irrelevant. Everybody has them and they don't prevent a server from working.

Also your Forge version is really outdated. The latest one is not 1291, but 10.13.4.1614! Though you should stay at a version level compatible with your server software if you use Cauldron or KCauldron.

You should post your server log somewhere (pastebin) for reviewing.