Hello everyone,

I have a situation where I need to grant two users access to a shared mailbox. I have granted User A Full Access Permissions to the shared mailbox, this Mailbox appears in Outlook and they can open/access it without issue. I then granted User B Full Access Permissions, and while the mailbox appears in their Outlook they receive the following errors when trying to open the mailbox 

If clicking the dropdown arrow beside the mailbox name 
"Cannot expand the folder" 

If clicking the mailbox name 
"Cannot display the folder. Microsoft Outlook cannot accessn the specified folder location. The operation failed. An object cannot be found." 

In examining the local PC's event logs, I see there is an event for this that says the following 

Information 
Microsoft Outlook
Cannot expand the folder.
P1: 300187
P2: 15.0.4701.1000
P3: 6xk3P4: 0x8004010F

Further to this, I attempt to grant User B access to another mailbox, and they receive the same errors. Essentially, User B cannot be provided Full Access Permissions to any mailbox. 

I can however login to OWA as User B, and open the shared mailbox from here. 

I have tried the following: 
- Create new Outlook profile 
- Disabling/Enabling cache mode 
- Outlook 2010 and 2013 
- Granting Full Access Permissions by command line (with and without AutoMap, and trying to map manually) 
- Granting Delegate Access to the shared mailbox 
- Granting Owner permissions to the shared mailbox, and subfolders of the shared mailbox 

Are there any thoughts on why this one user cannot gain full access permissions to any other mailbox?