yea sorry bad memory of the error. it was actually "incompatible version" this is with the whole firmware updated.
"Incompatible Version" implies that the whole firmware was not updated. This error is referring to the mpegplayer plugin, not to the movie file.
Ensure that the only copy of rockbox.gigabeat is inside your .rockbox folder (was it ever in the root of the player on the Gigabeat?), and double check that you have fully extracted a current build - overwriting all existing files.
A common mistake people make in this situation is to either not overwrite all files, or to extract a current .zip file
into their .rockbox folder creating a new .rockbox nested inside their old .rockbox - where it won't be found by the firmware.