I have encountered this in passing on our internal forums a few times… the issue being that “randomly” when users log in to Outlook they are missing all buttons, as though they aren’t enabled, and never have been.
One possible cause of this is that during the archiving process we synchronise the mailboxes, one of the things that that entails is that the current hidden message in the mailbox, containing desktop/archiving settings is deleted, and a new one created. The issue is that if the user has peeked over their Exchange mailbox send/receive limit, we can do the delete, but we can’t add the new settings.. Effectively disabling them.
The client trace usually looks something like this :
22/02/2011 20:20:24.700: Log file created (level 1).
22/02/2011 20:20:24.700: RPC over HTTP is not enabled (flags = 0)
22/02/2011 20:20:24.717: LoadSettingsFromHiddenMessage com_error: 0x80004005
22/02/2011 20:20:24.718: User is not enabled – hiding UI.
Exchange will go over the send/receive quota when system messages are delivered to the mailbox, amongst other scenarios.
To get around this issue in Enterprise Vault possible solutions include changing the archiving policy to quota, or quota + age.