I recently removed Office 97 from an XP Pro Client computer.
Unfortunately the removal of Office 97 can have unintended
consequences. A registry key is removed such that Outlook Express can
no longer register as the default EMAIL application

The following microsoft article provides more information
http://support.microsoft.com/?kbid=306098

I tried various permutations of the suggested /reg command.

Microsoft suggests:
drive:\PROGRAM FILES\OUTLOOK EXPRESS\MSOE.DLL

I first used:
"c:\program files\outlook express\msimn.exe" /reg
which had no effect on the key

then I tried quotation marks around the entire command
then I tried quotation marks around the individual folder names
then I created a batch files with the above commands with no luck

eventually I navigated to the directory and issue this command:
msimn.exe /reg

that was the only command that worked. Other than human error, is
there any reason why quotation marks didn't work? Could there be
something about the system environment that rejected quotation marks?
This question may seem absurd, but I have to ask.