Hi,

Just reference and develop with the Outlook 2003 PIA, the code will
run with no problems in Outlook 2007.

You are walking on unsupported grounds hers.
See this Microsoft blog:
http://blogs.msdn.com/andreww/archiv...of-office.aspx

MS officially supports Outlook 2003 COM addins running on Outlook
2007. Look at the information from the Outlook team on their blogs.

I searched "site:blogs.msdn.com VSTO Outlook 2003 support 2007" and did not
get any posts which indicate that it is supported.
As I do some COM programming where I need to version correctly when
producing new releases, I know how easy it is to break something. So with
the extra layer of PIAs and VSTO (which also needs correct versioning) on
top of the COM type libraries I am a bit uneasy to believe that everything
"just works" :-)

--
SvenC