Without more information or being able to test with your specific setup I can't narrow down a problem.
Most common causes: Mugen, screenpack, sound, character (P1 or P2), stage, computer memory, or video card issues.
I tested Enchantress and Green Goblin with my Mugen 1.0 screenpack and they work fine
I tested all modes in mugen 1.0 without any crashes.
Tips for bug testing:
Test the character in a NEW mugen (fresh download of the same version).
If the character works, add more elements (characters or stages).
If it still works try adding the screenpack.
Trial and error is the best way to find out what is causing the issue if you do not have a error or see an error to go on.