So far I can confirm that all pages with this error have a gallery, but all pages with a gallery do not have this error.
I think this may have something to do with my previous report of incorrect import of Caps due to the "shouting rule" setting. I'll check some more, but it appears as if the "shouting rule" does not affect text within any wiki tags like <gallery> or <span style>, yet it does affect the photo import itself. Therefore the image name within the tags is different than the image name itself after import.
I would hope this would not be an issue if the "shouting rule" was not in effect. But at any rate, the gallery tag with parameters does not appear to import/convert.