From the Troubleshooting Errors in Word Processor Documents page:

If you encounter a broken document, please create a new thread in the Zotero Forums so we can attempt to fix the issue. Be sure to include a Report ID from Zotero, your operating system and word processor versions, the steps you have attempted to fix the error, and whether you were successful. You should also send the document excerpt from Step 10 and a link to your forum thread to support@zotero.org so that we can try to reproduce the problem.

You haven't provided a Report ID and you haven't sent the document excerpt.

You don't need to create a new thread, and you don't need to email us to let us know you posted — you can just post new information here. I've merged your post back into here.

But you don't say that you've actually followed the last step on the troubleshooting page, which is the most important step. Unless you can delete everything in the document so that it's completely empty and still reproduce the problem, that step will by definition isolate and likely help you fix the problem.

Either way, you should email us a copy of the smallest section of the document that reproduces the problem so we can investigate.

No, you're misunderstanding that step. It's obviously not saying to delete your document. It's a troubleshooting step to try in a copy of your document, and it's explaining that, unless the error still happens after you delete everything in the document and try to insert a new citation in an empty document, then you can by definition follow the steps given there to quickly cut down the document in order to isolate a small section that's causing the problem.

But are you saying you get the error if you try to insert a citation in the excerpt of the document that you sent? You open that excerpt, click Add/Edit Citation, and get the error? That works for me. What if you delete the few citations that are there (23, 26, 27)? And what if you delete the entire contents?

I have no problem when deleting the in-text citations though.

Meaning if you delete "(23, 26, 27)" you can insert a new citation without getting an error? If so, what happens if you delete those same citations in your original document?

And what do you mean by delete the enite contents?

This is all just from the troubleshooting steps you say you've followed. From that page:

11. Isolate the problematic citations. Delete half of the document at a time and see if the error still occurs. If not, use Undo to restore the deleted section and then try deleting the other half. Repeat the halving process on the section that fails, or pick one at random if both do. Continue this until you find the smallest possible section, ideally with a single citation, that must be present for the problem to occur. Remove the isolated citations from the original document and the problem should go away (unless there are multiple broken citations, in which case you'll need to repeat the process). Unless the error still occurs if you completely clear the contents of the document, this final step will by definition identify the problem.