MBWE 1 TB White Lighte Copy manager problem

When I copy with Copy Manager some strange things happen:

i copy a file abc.wmv to (a documentary) the MBWE and try then to play the file: a completely different file (in this instance a ray charles video) starts to play!

When I copy that abc.wmv file back to a computer, it has turned into the ray charles video???

Something seems to be wrong with the FAT or so. Should I format the MBWE and if so, how can i do that?