files dissapears on SATA2 Hard Drive

On a PC, I have copied files on a 1,5 TB SATA2 HD that my colorist has installed in his Mac to work with.

He's currently having problem with folders and files dissapearing.
His computer is set for SATA, but is supposed to read SATA2 as well.

He talk with a store clerk, and he thinks it might have to do with drive addressing of his internal drive controler and maybe the HD jumpers.

He's curently testing overriding his internal controler with an external encasing and playing around with the HD jumpers.

Any other suggestions or person experimenting or having fixed this bug?

Any link or tips would be greatly appreciated.

External encasing and jumper didn't do anything.

I'm currently running scan for errors with my PCs and will then test is it's doing same thing to me and will also check on another Mac to try an isolate source of problem.

I searched web and found nothing regarding this issue so far.