A slightly different issue, but the following thread is another example of the sort of problems that can occur with TOD:
Yesterday a customer attempted to print a return ticket, purchased from the TPE website, at Mount Vernon station. The outward portion printed fine, but the return portion did not. The TVM stated an error had occurred. The Help Point at the station advised the customer to see ticket office staff...
www.railforums.co.uk
For future reference, if the journey being made is e-ticket enabled, I would recommend considering an e-ticket (which is issued as a PDF which can be shown on
any device and can optionally be printed, if you wish to do so)