biblatex --- to reiterate, I have been exporting to biblatex for the last 2 weeks or so with no issues.

Additional notes:
(1) export to bibtex and Zotero RDF works without error.
(2) (do not know if any of this matters) but I have restarted the browser, cleared the browser cache, and rebotted the machine --- none of these removed the error
(3) finally, I have tried exporting from Firefox and Zotero Standalone --- neither works ...

>> are you using the better bib(la)tex add-on?

Sorry, I do not know how to answer this question. Could you please elaborate?

I have Zotero Word for Window Integration Extension as an add-on (Libre is installed but disabled).

>> what's the error?

I assume @Dan will respond to you with details from the submitted error but here is what I see:

[Javascript Application]
"An error occurred while trying to export the selected file"

Thanks ... I installed better bib(la)tex ... the export succeeds but the citations do not compile correctly in Latex ...

I switched back to base bibtex to make it work.

[Wondering what triggered biblatex to suddenly stop working]

One last point: my storage was full when biblatex export started to fail (sync also failed). I have cleaned up my storage and sync successfully.

Thanks --- I can export to "BibLaTex" now.

On another note, I looked at the github link you posted and saw:

"[Bib(La)TeX] Convert all dashes in pages to double dash on export"

Dashes (and apostrophes) are indeed an issue as noted by DustinT (I commented on that thread too: https://forums.zotero.org/discussion/39509/apostrophes-and-dashes-turning-into-odd-characters-in-references/#Item_12

no, different error. If you're in a hurry, you can revert to an old version of the BibLaTeX exporter by downloading the file from here:
https://github.com/zotero/translators/raw/b91bf458ef97d06d7731cfc3c71d23af3659fa38/BibLaTeX.js
and using it to replace the file with the same name in the "translators" folder in your Zotero Data directory: https://www.zotero.org/support/zotero_data
Uncheck automatic updating for translators in the general tab of the Zotero preferences.
I hope we'll have a proper solution for this shortly, but as of now I can't replicate the issue.

I am having a Better Bibtex export problem now too. While working this morning, Firefox suddenly crashed out of nowhere. When I brought it back up, all my citation keys were missing from the Zotero entries. When I try to export the library using Better Bibtex, I get an error saying that the file could not be exported. I uninstalled all Zotero and Zotero plugins and then reinstalled. I still cannot export using Better Bibtex and all citation keys are gone. I am able to export the Zotero library without using Better Bibtex just fine. My library is large, and I have used auto exports from Zotero in writing a LOT of papers over the years. I absolutely rely on this functionality. Any ideas?

Here's a link to the Firefox crash report: https://crash-stats.mozilla.com/report/index/22a3185f-c46d-4e65-9108-9f7b02160627

I also sent a Better Bibtex bug report

The latter problem has since been fixed.