problem adding new managers to google+ page

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Project Description:
We have a Google+ page for our business that we are trying to grow, but I am not able to add any new Managers to be able to control the page.

Here is exactly what happens when I try adding a new a manager:

1) I type in the email and press Invite
2) It asks me to confirm, I press Invite again
3) It gives me the error message "[email] is already a manager of this page." (Which they are not)
4) I refresh the page and then [email] shows on the list as invited, but they never get the invitation and are unable to accept.

The only link I was able to find with the same issue is above and they claim it "fixed itself" eventually. (!topic/google-plus-discuss/NOjjte-Nt7g)

This happens with every single email account I try, so is not related to that specific persons account or email.

I've made sure to check that accounts being invited have selected "Receive invitations to manage Pages" in their account settings.

Social experts - how can we fix this?

Skills required:
Google Plus, Social Networking
Hire givememyleg
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givememyleg United States
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