Users cannot edit a shared calendar of a shared mailbox that was deleted from the cloud and recreated on premise

Question

Description:
The following example account [email protected] is an on premise AD account being used as a shared mailbox in the cloud. We have discovered that regardless of what we do, not a single user can edit the calendar entries.
The following message is shown in Outlook Click to Run 2013 when an entry. "New appointment" button is also greyed out, including "Calendar Permissions" and some others.
This problem started when the shared mailbox was created wrongly by creating it in the cloud first and we had to delete it and start over. The "in the cloud" user was deleted and the same user was created in AD on-premise with the same account name
and then Dir Synced with the cloud. A license was assigned, a user mailbox on exchange online created and the type was converted to a shared mailbox and Editor rights were defined on the calendar folder for specific users.
Actions performed:
Action01: gave users Editor rights on calendar folder through powershell
Result01: Rights correctly added and can be seen when get-mailboxfolderpermission is ran
Action02: Opened calendar with Outlook and tried to edit entries
Result02: Error message pops up saying "You don't have permission to create an entry in this folder. Right click the folder and check..."
Action03: Opened calendar with OWA of users
Result03: Users can edit the shared calendar on OWA
Action04: Gave users Full Access permission on mailbox with automapping on
Result04: Users can edit calendar in Outlook
Action05: Gave users Full Access permission on mailbox with automapping off (mailbox no longer visible in outlook)
Result05: Users cannot edit calendar in Outlook
Action06: Removed Full Access permission on mailbox for users
Result06: User cannot edit calendar in Outlook
Action07: Removed [email protected] from on-premise AD, performed dirsync, removed account from ms online using remove-msoluser -removefromrecyclebin
Result07: No trace of the account was anywhere to be found.
Action08: Created new [email protected] account on on-premise AD, assigned o365 license to user including exchange online license
Result08: New empty Exchange online mailbox was created
Action09: gave users Editor rights on calendar folder through powershell
Result09: Rights correctly added and can be seen when get-mailboxfolderpermission is ran
(Note: whenever mailboxfolder permissions are modified for this mailbox it's as if they are ran THREE times in a row, the first time they are applied and the powershell gives immediately 3 exceptions behind this:
An existing permission entry was found for user: [email protected]
    + CategoryInfo          : NotSpecified: (:) [Add-MailboxFolderPermission], UserAlreadyExis...nEntryException
    + FullyQualifiedErrorId : [Server=DBXPR05MB046,RequestId=3b3e080e-9aaf-4db9-9b90-b7171d59eba2,TimeStamp=7/11/2014
   8:15:39] [FailureCategory=Cmdlet-UserAlreadyExistsInPermissionEntryException] 57078FCD,Microsoft.Exchange.Manageme
  nt.StoreTasks.AddMailboxFolderPermission
    + PSComputerName        : outlook.office365.com
Any other mailbox does not do this when setting mailboxfolder permissions)
Action10: Opened calendar with Outlook and tried to edit entries
Result10: Error message pops up saying "You don't have permission to create an entry in this folder. Right click the folder and check..."
Action11: Tried on a fresh new pc with first time logon
Result11: did not help
Additional information:
We have seen this problem with another user which was recreated, when he shares his calendar with others and people get the calendar invite email and click "Open Calendar" they receive a popup "The folder cannot be found".
My first impression points to a corruption/bug in the GAL on exchange online, since we're using o365 for midsize bussinesses we cannot use the AdressList role to expose the adresslist cmdlts for deeper troubleshooting.
PS:
Issue tested on different computers and with different user accounts, not a single user can edit the calendar of [email protected] when editor rights are given.
Noticed when editing rights for the shared mailbox in powershell after the first confirmation line
Office 2013 is click to run was updated to latest version, version number: 15.0.4659.1001

Answer 1

Greetings Gil,
I haven't heard of that one.
Questions:
Does the calendar in question show up in the "Subscriptions" category of iCal?
If you remove all accounts from iCal > Preferences > Accounts and quit and re-open iCal, does the calendar in question vanish? If so, does the calendar come back when you re-input the servers you need into  iCal > Preferences > Accounts?
Can you provide a screen shot of your calendar sidebar.
While you answer those questions, some troubleshooting to try:
Try dragging one of your other calendars above this calendar that won't delete and then quit / re-open iCal and attempt to delete the calendar in question.
Failing that:
1. First make an iCal backup:  Click on each calendar on the left hand side of iCal one at a time highlighting it's name and then going to File Export > Export and saving the resulting calendar file to a logical location for safekeeping.
2. Go to iCal > Quit iCal
3. Remove the following to the trash and restart your computer:
Home > Library > Caches > com.apple.ical
Home > Library > Calendars > Calendar Cache, Cache, Cache 1, 2, 3, etc. (Do not remove Sync Cache or Theme Cache if present)
4. Launch iCal and test.
If the issue persists at this point:
Remove the following to the trash and restart your computer:
Home > Library > Caches > com.apple.ical
Home > Library > Calendars > Calendar Cache, Cache, Cache 1, 2, 3, etc. (Do not remove Sync Cache or Theme Cache if present)
Home > Library > Preferences > com.apple.ical (There may be more than one of these. Remove them all.)
---NOTE: Removing these files may remove any shared (CalDAV) calendars you may have access to. You will have to re-add those calendars to iCal > Preferences > Accounts.
Hope that helps!