Clickonce failing during upgrade

Trying to test upgrading my clickonce application. First one installs fine, but next one fails. I get the dreaded "A device attached to the system is not functioning. (Exception from HRESULT: 0x8007001F)". I use the clickonce "Data Directory" path to store files. I believe the problem is that during the upgrade, the clickonce installer is trying to do its documented function of copying the previous version's data files into the new data directory. It can't do it probably because of some permission issue, so it fails.

I don't get why there would be a permission problem, as I was the same "user" when I originally installed vs. when I now install the upgrade?

I've seen a ton of responses that say use "LocalApplicationData" for a myriad of reasons, and that's fine, but I need to figure out a way to get this Data Directory storage use working as it is documented.