Asking you to downgrade the firmware to a version which does not even support the most recent hardware version seems like clutching at straws, unless Humax believe all firmwares since 1.01.09 contain a bug which could result in what you are seeing (presumably in the DLNA server).
I'm sure we would know about such a problem; we are aware of a network conflict, and we are aware of problems with corrupt files, but we know how to regain control without resorting to 1.01.09. You would have thought Humax should have a wider knowledge of reported faults and remedies than we do!
However, that said, 1.01.09 does sound like a useful diagnostic (but not a permanent solution).
I think it was a case of getting me off the phone really quickly, He, humax rep, sounded quite confident that it would fix the issue. When it didn't work I phoned them back up again and the person i spoke to was not willing to go through it step by step with me because he said its quite simple and the instructions are in the email and was written by a member of his team. Although I do agree that they were simple to follow I thought that maybe I did something wrong because the 1st rep i spoke to seemed confident that the solution would work.
He did however tell me that if I couldn't fix it and wanted all the same features then I should maybe look at the 2000T or T2000 (can't remember which side the T was on) because it offered all the same functions as the fox T2 and is pretty much the same thing but in a different outer shell.