I have no way to log into classic wow as I am apparently missing a second drop down. I only have account selection and not version selection.
Hello Heritage 
Sorry to hear you’re having issues with the Battle.net app… let’s clear out the app’s cached data to make sure it isn’t an update behind, or relying on outdated cached info.
Re-run the app and it should check for updates 
I’m having the same problem and none of the suggested “fixes” (deleting cache, deleting battlenet folder, etc) are working. I also get a BLZBNTBNU00000006 error when uninstalling through add/remove programs. Needless to say this is incredibly frustrating.
Nevermind, just reinstalled the app from a fresh client package. Everything’s good