Re: Saving a Photoshop CC project from a Mac (in .PSD format) to a thumb drive and trying to transfer it to a Dell laptop with Photoshop CS6. Will not open...Error message: could not complete your request because it is not a valid photoshop document.

The file was corrupted somewhere along the way (assuming it was still readable on the Macintosh).

The platforms don't matter, but you still need file transfer that doesn't corrupt files...