ok - with gmsmith's assistance, I was able to get this working!
here is what I did:
as the zimbra user, i ran
Code:
zmprov ca testadmin@mydomain.com password zimbraIsAdminAccount TRUE
and then I was able to log in to the admin console!
previousely, when just trying to change the password for the admin@ account, it was still not working. Creating the secondary admin account did the trick though!