NIS 2010 - cannot send Outlook 2003 emails

Windows XP, Outlook 2003, both clean and up to date -  

 

I have my "immediately send emails" option off such that I can carefully control when they are sent. When I let emails sit in my Outbox untouched, all is well, and I can send them from there whenever I need to with no problem. If I re-open one to alter or even review it, however, it will thereafter forever refuse to be sent - it just sits in my Outbox until it is re-copied into a new message and sent without ever being re-opened. The exact same behavior has been exhibited on both my laptop and desktop since upgrading both from 2007 to 2010. I have dutifully followed instructions to uninstall and reinstall, but both machines still have the same problem. Please toss me a bone here!!!!????