Error messages when adding plugin -- Are you sure you want to do this?

New multisite implementation with only the primary site so far. Using https.

When I attempt to add a new plugin, I have to re-authenticate, and then I get taken to where I see ONLY "Are you sure you want to do this?"

No opportunity to say yes or no. Dead end. Can't provide you with access -- I click Grant Support Access, have to re-authenticate (annoying!) and am taken right back to the support page with the gray Grant Suppiort Acces button. Wazzup with this??