Address insertion using MS word

I jusy upgraded to Office XP Pro and inthe process of trying to insert an
address using the envelope function I get the message - "Either there is no
default mail client or the current mail client cannot fullfill the messaging
request. Please run
Microsoft Office Outlook and set it as the default mail client."

Microsoft Outlook is already set as the default mail client.

To compound the problem (maybe) I use O.E. as my main mail reader, So I
deleted both account in O.E. thinking that would solve the problem, but it
didn't.

Any help would be appreciated.

Thanks
Kent