Tip: If using the BUG Option to limit stack sizes and get an endless WFoC you can get out of it without restarting the game if it's because of Stack Limits.
1. You'll notice that you can move the map around with the arrow keys or by the edge of the screen while the "Waiting for other civilizations" flashes without pause. This indicates that the WFoC is due to Stack Limits.
2. Press CRTL+ALT+o, or the Ladybug button if you can hit it.
3. Change the Stack Limit to a higher number than you have. 1 is usually enough but do 5 higher or remove limits for the turn.
4. Exit BUG and wait for the turn to finish.
5. Enter BUG again when it's your turn and set the Stack Limit back again.
Cheers
Tip: Just say no to stack limits (at least for now). The AI has no clue how to cope with them, and will be considerably less effective with them in force at any but quite high levels (at least 12-15).