sitemap errors that appear, disappear, reappear...

I have had an xml sitemap for some time, it has been crawled by Google
without a problem. I recently added a text sitemap, which was crawled
several times with no errors. Then, a few days ago, several pages were
returned denied, as not being under the sitemap path. They are, I
didn't know what to do, so I did nothing. The next crawl, no errors.
Now THIS crawl, same error, but different pages. What's up?