The game can't be quit normally. Whenever I exit the game, I get stuck on a black screen that never goes away. The only solution to get rid of it is to restart the PC. Task Manager does not show up, not even the CTRL+ALT+DELETE screen. Everything seems to work normally behind the black screen, but you can't get rid of it.

I am getting around it by quitting the game through Task Manager and never clicking the exit button. But does anybody know how to get rid of this issue?

I have had the same "black screen" issue with League of Legends, so it's not unique to SpellForce (yes, I have had the same issue with SP1 too).

My long-term soluton was playing all the games I can in windowed mode, as I have a screen resolution not supported by most old games, which I presume was / is the cause of the problem.

One thing worth checking though: open Task Manager, click Options and make sure it's set to "Always on top".
This way, should the issue occur again, at least Task Manager will be visible and usable.

If you want to try playing SP1 in windowed mode too, right-click on the shorcut to the game and add at the end of the Target box
-window

OR

-windowmode