What is QuickTime "unknown error (-50)"?
That looks like a classic Mac OS error code. After a bit of googling I came up with: 


  -50 | paramErr | Error in user parameter list


Which indicates there is an bug in the program. You should contact the developer about the issue.

It is possible that there is a command line flag that is incorrect and causing the issue.

Reference: http://support.apple.com/kb/ht1618