Error "Error while preparing to send sharing message" is displayed when you try to share the calendar in Microsoft Outlook

I have been working on this issue for weeks.  I have tried so many things and still can't resolved it.  This is my environment:

1 Windows 2012 server that is a domain and controller and its also an Exchange 2010 server.  This is for a very small non-profit organization.  

2:   This was not an upgrade of any kind, its a fresh install of the OS and Exchange 2010.

3:  Every exchange service works perfectly.  OWA, Autodisover etc.  Their smartphones can send/receive mail.

4:  This is a valid SSL cert installed.

5:  Everyone in the company has full access to everyone else's calendar.  

6:  I have a default sharing policy setup with everyone associated with the policy.

7:  I have checked DNS, and Active Directory, no errors.

If I log the users in the OWA they are able to share their calendars without any issues.

When the users go into their Outlook 2010 and try to share calendar with anyone else in the company they receive the error:  "Error while preparing to send sharing message"

I am not  sure what else to do  

Error Message
Chad FranksSenior System EngineerAsked:
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Amit KumarCommented:
Can you test if EWS is working, just right click on outlook icon in Task bar then do test e-mail configuration. see if there are any errors.
Chad FranksSenior System EngineerAuthor Commented:
no errors in the test email configuration.
Amit KumarCommented:
Try outlook configuring in Online mode rather using Cache mode.

If you are using outlook in online mode then use it in cache mode.

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