I did the following:
1- Went to https://code.google.com/apis/console
2- In the "API Access" page, I chose to create a new browser key
3- In the referers list, I added the following: https://MY_DOMAIN:7443
4- Went to advanced and put my new key and saved
Still I got the same error message. I also tried the following referers
https://MY_DOMAIN:7443/zport/dmd
And I also tried to sign out and then sign in again as mentioned right next to where I put my API key in Zenoss. I also tried to clear my geocode cache, but all in vain.