We are running SW2015/EPDM2015 and have been using "Paste as Reference" for a couple months now to capture specification data. Everything has been working fine until today. 

I had an engineer ask for help attaching a PDF to the SLDDRW. Normally it's a simple operation of checking out the SLDDRW and pasting the reference file. I'm now getting the warning shown in the screenshot and cannot go further. There is no description at all of the issue, so I don't know where to start. Everything was done the same as we have been for months.

Any ideas are appreciated.