Never mind, found the problem.
Seems the checksum was not being updated on the edited file when trying to restore.
Found a Perl script (below) that recalculated the new checksum for me, when I put this in the file, the edited file could be restored and now muticast works. I had rather presumed that FBEditor 0.7 would have done the checksum work for me.
BT IPTV (YouView) now confirmed working on 7490 with Fritz!OS 6.52.
link to checksum script
Edited by zippysticks (Fri 01-Jul-16 10:54:20)