Permission issues Ex2013 shared calendar with Ex2010 mailbox

​​Scenario: A user with a mailbox in Exchange 2010 is getting permission errors in Outlook when trying to access and edit a shared calendar of a mailbox in Exchange 2013 even though the correct permissions are set for that Exchange 2010 mailbox. The error is:

"You do not have permission to veiw this calendar. Do you want to ask user to share his or her Calendar with you?"

Resolution: Enable Outlook to connect to Exchange using HTTP for the Exchange 2010 mailbox in the Outlook Profile

1. Start Outlook if not started already.

2. Navigate to your Outlook Account Settings:

a. Outlook 2013/2010: Click on File --> Account Settings--> Account Settings.
b. Outlook 2007: Click on Tools --> Account Settings.

3. Select your Exchange account, and then click Change.

4. Click More Settings, and then click the Connection tab.

5. Under Outlook Anywhere (Exchange over the Internet for 2007), select the Connect to Microsoft Exchange using HTTP check box.

6. Click Exchange Proxy Settings.

7. Make sure the following settings are set:
a. Enter the URL to connect to  proxy server for Exchange: https://mail.domain.com
b. On fast networks, connect using HTTP first,... is checked.
c. On slow networks, connect using HTTP First,... is checked
d. Proxy Authentication Settings is set to Basic Authentication.

8. Click OK to close each Outlook window.

9. Restart Outlook

10. If your are prompted for authentication, use the following:
a. username: domain\username
b. password: your password.