Cannot log into Messages I can no longer log into Messages. It normally logs me in automatically, but now it didn't log me in and the entry in the menu is greyed out. I am connecting to the internet from a different network than usual. How do I fix this? 

I run OS X 10.9.5 and Messages Version 8.0 (4226)
Look at your preferences and make sure that the account is properly enabled.

If it is, try signing out and signing back in to see if that solves the problem.