I have the inability to ban online or offline players, when I attempt to do so I receive the message "Error: Null" and no error message related to it in console.
I'm also having a similar issue with GroupManager, whenever I attempt to promote, demoted, or run any command on an offline user I receive the message "An internal error occured while attempting to perform this command" and this error in console: https://gist.github.com/anonymous/12c0b45ab3ed2808c507
Although a server restart fixes both issues, this is only temporary and does not last long.
Start-up log: https://gist.github.com/anonymous/2b6062fc22af35d3bed8
Ubuntu 14.04.1 LTS
OpenJDK Runtime Environment (IcedTea 2.5.4) (7u75-2.5.4-1~trusty1)
OpenJDK 64-Bit Server VM (build 24.75-b04, mixed mode)