Problem with Custom Permalinks

I have several clients using WordPress for their sites, and I like to set them up with the following custom Permalink option:

/%category%/%postname%/

and it works fine except on one site. I recently moved their WordPress from a sub-directory to the root directory by following the instructions under “Moving WordPress” in the codex. However, they wanted the blog portion of their site to remain in the original sub-directory. (This is how my personal site is structured and it works fine).
But now, when clicking on the “Blog” link in the menu bar, it returns the following error message:

Not Found
Apologies, but the page you requested could not be found. Perhaps searching will help.

This is the URL: https://sjdemocrats.org/blog/

However, if I click on the “View” link on the “Posts” page, I can see individual posts at urls like this:
https://sjdemocrats.org/uncategorized/40th-ld-4th-annual-fall-social-potlu/
or archives like this:
https://sjdemocrats.org/2010/07/

Any ideas on what I need to do to fix this?

Thanks!