The error message "Command failed" is often associated with a bad EndNote field code in the Word document.
To test if the problem is with this specific Word document only, please create a new, blank Word document, and insert some references. If this works ok the problem is probably with your specific Word document. If this gives same error message in new, blank Word document, the problem is more serious and you probably need a reinstall of your Word/Office application and then a reinstall of your EndNote.
1. Check your field codes (at the end of your document/bibliography)
The first thing I would check is to toggle on the field codes to display (Word: File > Options > Advanced > [Show document contect-section] > "Show field codes instead of their values"], and scroll to the end of the document to see if the Bibliography code has separated from the bibliography. The bookmark should appear at the beginning of the bibliography, with a seeming plain text bibliography following it.
Delete the bibliography, and the code, and see if the document will update.
Please remember to turn off "Show field codes instead of their values" after you have done this.
2. Unformat and check your citations (in the text)
If the bibliography appears properly packed into the bibliographical EndNote bookmark at the end of the document, the next thing to try would be to highlight selections of the document containing citations, and attempt to unformat them in small batches in the document (Word [EndNote]: Convert citations and bibliography > Convert to unformatted citations).
Actually highlighting a portion of the document, and choosing “Convert to Unformatted Citations” from the Cite While You Write tools will only unformat the citations in the selected text. This should allow potential pinpointing of the citation (or citations) in the document which may have damaged codes.
3. Unformat the whole document and paste into new, blank document
Please see our support article Solve issues with EndNote references in a document for the needed steps to do this.