Error code -50 or -54 seems to be caused by having multiple copies of Toast Titanium 7. If you get this error, you may not be allowed to save a toast disc image or use file save function. Fixing file permisssions with DiskUtility may not fix the problem. In fact, a simple solution seems to work by just throwing away the following files:

com.roxio.Toast.plist
Roxio Toast Prefs