That's an unhandled exception in the program, so it's hard to say exactly what's going on there. If you are a programmer, you could attach a debugger and see what it's doing, but I'm assuming you're not.
So if it did work before, you might first want to try
Unzoone to fully remove all traces of the Zune software and then try reinstalling. If that doesn't work, you could try
this KB article - this has cured some users' crash-on-start problems before.
It's a generic error, so I'm afraid I can't give you any other specific solutions, but good luck