Codebuilder failure after being dropped from world

A student was in a world hosted by another student. He was working in his code builder and the host booted him from the world. At this point his code builder would not work in any of his own world. Code builder hangs with the animated agent walking icon. We tried restarting Minecraft but he still cannot access his code builder. 

UPDATE: after rebooting Windows, he was able to access Codebuilder.