Copy paste works on one file but not another

[MillersportCustoms]

Just had this start happening this morning. I'm running CS6. I have two image files open. I can make a selection on one image file, Ctrl N for a new file, and then Ctrl V and my selection pastes to the new file as it should. Go to other image file and do the exact same thing, and what I have selected does not copy and paste. In all my 20+ years of using Photoshop I've never had this issue before. Any help?

[Kevin Stohlmeyer]

@MillersportCustoms check to make sure you are comparing similar documents including layers, bit depth, canvas size, etc.