unable to validate serial number

We have Acrobat DC 2017 with volume licenses. On one of the installs, when launching the application a window comes up reading: :Unable to Validate Serial" number.

I called support (if that's what you call it) After being transferred to 7 different people and verifying the account, I finally get to some guy named "Kaushik" who refuses to help me because he cannot validate the account.

So I turn to the real experts, the user forum.