A user told me that he had an issue to access a shared mailbox via OWA but there was no issue to open it via Outlook…
When accessing with OWA, he got that error :
The user was not having a permission issue as he was able to access it with Outlook and I could with PowerShell that he has FullAccess permission on it.
I gave myself Full Access on that shared mailbox and I got the same error…
After googling a bit, I found that this error was really generic and found multiple solutions like if there was a moverequest flag you could get that error but this was not the case.
Then I saw that the principalsmtpaddress was having an “&” character, so I replaced the email address in the URL by an alias without any special character and… I was able to access it !
The moral of the story, beware of the special characters !