I have a DVD that will not play back properly - the picture is broken up
into multi-coloured blocks, occasionally clearing up for a split second
before reverting to the blocks. The DVD plays just fine on my DVD
player and on a friends Windows box, so I am assuming that this is
either some sort of copy protection or a codec issue.

How can I find out what the problem is and whether I can fix it? This
is the only DVD I have any issues with - and it's one of my favourites