Calendar can’t save the attachment '' to the Exchange Server - OWA, MAC Calendar and Iphone Calendar could be failing

Delete the calendar entry and start from scratch.

This has happened to me twice and in both instances it was the prelude of a bigger issue, the Exchange/Domain password expires but the error is not shown because Microsoft products cache credentials in a way that some services might still work with old passwords (caching).

In fact I have seen that the Calendar stops working even from the Outlook Web Access (OWA): I was able to interact perfectly fine with emails but my Calendar was unable to show my events.

Unfortunately this time my OWA, iPhone and MAC calendars all failed to me for three days until I realized this. Even though it was the second time it happened to me, the first time I did not realize the root cause of the problem but now I recalled this was exactly the case.