My signwriter can't open my new files "locked or invisible"

Hi my first post here. I've had a "trial" version of X5 and created some simple electronic equipment control panel labels for my signwriter/engraver and all was good. Since buying a license he tells me he can't open the new files and gets an error of "Corel Draw is telling me that the active layer is locked or invisible"

I've redone the files from scratch a few times but still the same. I'm a novice with Corel but can't see any difference in files that work or don't work on my pc when I view properties and object manager. I believe the license was activated with Corel so think that should be OK. I don't know anyone else using Corel so I was hoping to attach some cdr files to see if anyone here could help or advise. Hmm just tried to attach a file and its limited to 256k, both files are about 500k. What do users do for large file sharing on this forum?

Thanks in advance Joe