Proxy problem, empty folders

Hi Forum,

we set up up proxy access for two account's (User A and User B) to another (User C). They have different rights, but both have all "read" checkboxes checked.
The difference is, that User A sees only folders and no mails, appointments etc. For User B all mails and other objects are visible.

Anyway, I will find mails if I do a search with User A in the mailbox of User C. I can also open the mails and read them.
If I go to the folder directly in the client, then the folder appears empty.

The access was configured some days ago. I know it can take some time, until mails are visible. Should not be the case here...

Any suggestions?

Thanks in advance,
Pascal