I'm getting this same error message. Once a year I export all my notebooks to an external drive, as a safety backup.
I keep getting the failure above on some of the larger notebooks. But what is weird, is that let's say it fails at about 45% of the way through a particular notebook. I then go back to that same notebook and try again, and it ZIPS through to the 45% mark (where it failed the last time), and then SLOWLY starts ticking off the next notes.
It may fail several times, but it eventually gets through to the end.
But I have also noticed that the export process has become VERY slow. It always used to export really quickly, but I estimate that it now takes about five to ten times as long to export the same notebooks as it did the last time I did this process. And I have a faster computer now than I did then! So something is definitely up.
One of the notebooks has about 50,000 notes, and it's failing consistently around the 10-15% mark. It may take me forever to export, but I keep trying again and again...
Sigh...