Mail could not be sent Error Code -18500

Hi guys,
Getting a quite unique issue with a delegate not being able to delete an appointment from her managers calendar

The Manager has a PC running Office 2010 fully patched and the PA has Outlook for Mac 2011 fully patched
I have used the Managers Outlook client to set the delegate permissions and opened the Calendar on the PA's Outlook for Mac

We're running MS Exchange Server 2010

The PA can accept appointments but can't then delete them, the error is below

HTTP error. The server cannot fulfil the request
Mail could not be sent
Account name <NAME>
Error code -18500

I've duplicated this issue on other machine so I know its not a client issue

OWA produces the error below
An unexpected error occurred and your request couldn't be handled

The PA dosnt have send on behalf permission or full mailbox rights

Any help would be great
Question Info

Last updated March 26, 2018 Views 749 Applies to:
I found this page that had some details about a solution:
It looks like a timeout error with the exchange server.

MVPs do *not* work for MS
Les MVP ne *travaillent pas* pour MS

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