On a computer that is running Microsoft Windows Vista or windows 7, you cannot write an new email or reply to an email. other problems include..
1) Compose a new email
2) Reply to an email
3) Setup a new contact, task, note, journal entry, or appointment
4) Change any settings in the Outlook Web Access options folder
On a computer on which you have installed update 912945, you must first click one time in the compose frame in Outlook Web Access before you edit text. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
912945 (http://support.microsoft.com/kb/912945/ ) Internet Explorer ActiveX update
This is a know issue on your exchange server.
To resolve install the Microsoft patch 911829 on your Exchange servers. Click here for link to download page.