I have two users within the company that seem to be running into an issue each time they try to access the public folders.
They receive the following message: Cannot expand the folder. The set of folder cannot be opened. Microsoft Exchange is currently busy. If this message is still displayed in 30 minutes, contact your Exchange Administrator.
I have assigned the same public folder access to myself and it seems to work fine for me.
I cannot seem to find the public folder within the owa version of outlook either, for the users in question.
I have removed the user's access and waited for about 2 hours, reapplied access to the folder and still nothing.
I know this has been a while. Would you be in an hybrid environment? We did experience the same mostly for users having multiple additional mailboxes .. it looks like if the PF is opened with a different ID (one of the additional mailboxes) that the primary one, the PF permissions used for opening the PF is from that additional mailbox ..and does not have the permissions to open your primary PF tree...