[nichol2]

Originally Posted by BetterRed

That msg originates from Windows, says it can't create a file, but its odd that it is only some file types, try turning off your AV.

Also try downloading this file https://manual.calibre-ebook.com/calibre.pdf to your desktop, then drag and drop it into the calibre book list, viz:

Attachment 168370

BR

Turned anti-virus off and the problem disappears, thanks!

For now I'll use that as a fix, though it's far from ideal.

Dragging the PDFs directly into the device is also an option but I often lose bits of pages that way.