When starting Outlook 2007 and attempting to send new e-mail (compose a message) you might get error message "A dialog box is open. Close it and try again.". This alert appeared even though no dialog boxes appeared to be open.
The problem is that Outlook started on a new user profile, and the usual Outlook/Word dialog that asks you for your Name/Initials was getting hidden someplace (because Word starts silently in Outlook).
The solution is to close everything, restart the computer, open another Office application (like Word) and fill in the User Name details dialog box.
Once this is done Outlook will work correctly.
If you don't have the full Office installed, you won't be able to launch Word.
So to fix it, you'll have to temporarily remove a Microsft Update item number KB946983.
Use the control panel to remove this update, start Outlook, then windows will apply the update again at a later time.
Last option is to install following hotfix: