For a lot of problems, MS have a good solution list page here… otherwise, keep reading.
Ok, so this is not to recent but recurring issue – in particular with this symptom:
When using Outlook Web Access (OWA) from Internet Explorer 7, all appears OK until attempting to create a new message or reply to one. What happens here is when then new window loads, all points of entry (text boxes etc.) are disabled with a red x on teh top left corner… so here’s the proposed solution to sort it out:

Microsoft Hotfix 911829

Now the solution apparently causes more issues for some users. It has been reported to sort out the previous issue, but resulting in IE crashing at a similar point to the previous problem… so here’s the hotfix to sort that out:

MS Hotfix 924334

There is also a reported client side fix so if you want to try it first, here it is:

  1. In OWA, click on the “options” in the left Task Pane.
  2. Under “E-mail Security” and Click Install or Upgrade the S/MIME Control. This will download a new add-on.
  3. Click “RUN” when asked about the Microsoft Outlook Web Access S/MIME install and security warning.
  4. Close and RESTART IE7

I’d love to take credit, but can’t –