The only way to get this toolbar button back is to go into Add/Remove Programs>>click change on Microsoft Office 2007. Then under the Microsoft Office Onenote, you will see an Add-In field, expand it and you will see options for Outlook and Internet Explorer. CLick on the Outlook listing and make sure Run from My Computer is selected and then click continue. The next time you open Outlook your button for Send to One Note will be back and functioning.