Soft Encode has a so called "dying bug" that can occur if you canceled a conversion. Afterward it'll just keep crashing.
The fix is to delete two registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Sonic Foundry\Soft Encode
HKEY_CURRENT_USER\Software\Sonic Foundry\Soft Encode
HKEY_LOCAL_MACHINE\SOFTWARE\Sonic Foundry\Soft Encode
HKEY_CURRENT_USER\Software\Sonic Foundry\Soft Encode
Remove these and it should start to work again.