Thankfully, I haven't touched Outlook in years, but this error would make me think the problem is on your end:
"Outlook is unable to download folder (null) from the IMAP e-mail server"
- Especially since webmail is working fine for you.
If you have a firewall, or something like Norton Internet Security, you could turn that off and try again. If it works, you'll need to adjust firewall settings.
If it doesn't work, you could reboot the computer if you haven't already tried that... in case it's just Windows or Outlook acting up.
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