These are all the Errors and possible fixes that I am aware of. If you would like to add to this list please PM me.
Multiplayer Specific:
None
Zombies Specific:
Crash when you press Online button
- You cannot play online anyway, ignore and play solo/custom match.
Global Errors (MP & ZM)
Error: Trying to get version of a demo when the demo system is idle.
- No fix yet, wait for the update
Crash when trying to press the first Online button
- Sometimes this happens, restart, run as admin. Use the arrow keys and go into options, if it doesn't freeze then press ESC, and arrow up and press enter on the Online button. Should now work
Black Ops II Servers not available
- If you have a non-english version (Russian/German) please download the english files - English is the only supported language!
Crashing when I try loading a DLC map
- You may not have the DLC, even though it shows up. Please go and download them (Use Google, I'm not providing links)