Below are some possible steps you can take to access your archive mailbox in Outlook:

1. Restart Outlook
2. Check if the archive mailbox is set up on the client
3. Check if the mailbox is enabled for archiving
4. Verify if the archive mailbox was granted permission to Outlook
5. Check if the archive mailbox was moved to a different mailbox database
6. Verify if the archive mailbox is backing up to the specified location