WDTV not showing all mkv files (missing >2.5GB files)

Cannot see mkv files over 2.5GB in size from Laptop running Win 7.

All smaller mkv files OK.

All mp4 (any size) OK.

Cannot see any media shares from PC running Win XP Pro.

Connected wirelessly to router.

Laptop and PC both connected directly to router.

If Laptop disconnected from router (just using wireless connection) cannot see any files from media share either.

Have you tried a different wireless adapter or a wired connection?

What firmware does the WD TV has?