I was on my friends lan server when i placed a sign. It kicked me because of a java exemption thingy. He was still online but i would get the same error every time i tried to join. When he removed the sign everything was back to normal.
Environment
MacBook Air (13-inch, Early 2014)
intel i7
8 gb ram
intel hd 5000
osx 10.10.3
java 8 update 45
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-82968. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.