I have 2 fonts installed outside of the standard fonts. I find it hard to believe that would be a contributing factor.
*note the file uses 2 typefaces, one being a Windows default font and the other custom.
To test the number of applications thought, I've closed all but Designer, browser window, and one other application and I'm getting the same error with Designer as I was with publisher about access to the file being lost.
What could be causing the application to lose access to a local file? This seems to be the most critical issue. The secondary error has been hit or miss in my testing today.
The fun part is, after taking the time to rasterizing all of the linked images to pixels to try to reduce the number of open documents with it... When saving I received the above error too. So all of the layer conversions were lost on 45 pages.
I've seen others with similar issues, but I've not seen anything regarding a resolution or consistent workaround.