Did you try the steps in this support document?
https://support.clarivate.com/Endnote/s/article/EndNote-Mac-COM-exception-error?language=en_US
I assume you can’t unformat the citations to plain text?
But, the first thing I would try a new document with the style to be sure it isn’t the style.
Next is to copy and paste the content to a new document, without the bibliography.
if that fails - try copying 1/2 of the document – then the other 1/2. By this stepwise, you can try to isolate the portion that contains the part that has a corrupt code or field.