Error Message "program trying to access e-mail addresses"

Everytime I select "new" to create a new email I get a dialogue box that pops
up and tells me that "a program is trying to access e-mail address you have
stored in Outlook. Do you want to all this? If this is unexpected, it may be
a virus and you should choose No". I always choose "No" and am able to
proceed normally. I've running Outlook XP with Office SP3. I am also always
running NAI Vscan version7 with the latest dat and enginea and I've got all
scanning options turned on for all file types, so I am pretty confident that
a virus hasn't snuck into my computer. My question is, upon recieving this
error message is there any way to determine what program is trying to access
my addresses (i.e. my email editor aka MSWord, or a virus)?

Thanks in advance.