Text box not appearing in a Messages conversation I have a recurring problem in Messages on my Mac where, in one group conversation in particular, the text box occasionally disappears. Instead of having a text box at the bottom of the screen I can type into, the conversation simply goes all the way down. When this happens, the text box still appears in every other conversation; I can also still send messages in that conversation from my iPhone. It disappears only on my Mac, and only on that one conversation. The problem persists when I shut down Messages and start it back up. Sometimes the text box comes back, and then later disappears again, on a pattern that I have not been able to discern.

Any thoughts?

Messages 8.0
Mac OS 10.10.2
From another site, try disabling and then re-enabling the account in question as follows. 

Within the Messages app:


Select the conversation that has the problem (I don't know that this is necessary, but I did it anyway)
Go to Messages->Preferences...->Accounts
In the box at the left hand side, select the account in question -- it will probably be your Apple ID with "iMessage" below it
Then over on the right, make sure "Settings" (and not "Blocked") is selected near the top
Still on the right, underneath your Apple ID, uncheck "Enable this account"
At that point, back in the main Messages app you should see the text box reappear at the bottom of the conversation
Then re-check "Enable this account"


Done.

P.S. This was done on OS X El Capitan (Version 10.11.1), and Messages app version 9.0 (5084)