iMessage frozen/crashing

I have an iPod Touch 5th gen and I sent a really long emoji message to my friend and both our iPods froze! Now everytime I try to open it, it goes to the conversation menu, freezes for about 10 seconds, then crashes back to home screen.

I tried:

• Restart
• Long Restart
• Double clicking home and closing all recently used apps
• Turning off imessage then turning it back on and logging in
• Going to contacts then clicking to iMessage them

Nothing works.

I just had the same problem. After seething my iPad and restoring it through icloud I still wouldn't work but what did work was going to a random contact and clicking send message, it opens iMessage right up and I was able to delete my conversation that was causing the problem!