Send>To>Email Recipient broke. How to fix?

I have encountered something like this problem before and finally got fixed, but this one has me stumped and I need some help.

This is a dell optiplex running Windows XP Pro in a business environment. One of the applications is used to generate bookeeping reports, which then can be dealt with in a variety of ways, one of which is to ship them out to a recipient via email. That function did work, but doesn't now, and here is the behaviour:
- When you hit the 'sent-to email recipient' function, it does successfully invoke Outlook Express [which is what the person uses]
- and the little freshly-minted message box pops up.
- but any move you make to put an address in the To: field fails. you get the Windows audible "goof" alert, but the little OE window is essentially a zombie
- you can't close it peacefully... can't close the bookeeping app, can't close the OE window. have to kill them with Task Manager and at least once even that didn't help, the machine would not restart or shutdown. Had to pull power

And disappointingly, windows is not generating an Event for these instances. nothing in the log related to the issue whatsoever.

There are lots of notes laying around the nerdsphere about the entire invocation process failing.... in other words, the application loses its relationship to the default Mail package, as though it had never been setup. but that is not the case here - its picking the right package, but the functionality is getting halted.

????? I'm running out of ideas! help me