Failed to save document

I've encountered this a few times .

During the Auto-backup, the document failed to save in the background.

I can't do anything about it.
If I try to close the document, it'll prompt me to save it, leading to the same failure.

So I can only quit CorelDraw without saving the document. 
And if I reopen the same file, same thing happens.
So I end up recreating everything. 

It only happen to the particular file and not others.

Any idea what's the issue that causes this?