I think i may have found the soultion to our problem chaps.
there is a recognised issue with many media centres have problems playing mp4 and avi files OVER 2 GB in size.
Try either splitting your mp4/avi with biosoft video splitter or suchlike software and it should play fine.
alternativly mkv files over 2GB should work fine, providing there is no file corruption and your device supports the encoded format.
Hope this helps you all, please reply with results let me know if it works.
Happy viewing , Armyman