McAfee Firewall doesn't like Outlook

I am running McAfee Firewall Plus on my Windows XP PC and have an intermittent problem with it prompting me when I open MS Outlook 2003. It states that
"The Application Has Been Modified. MS Office Outlook has changed since you first gave it access to the internet. Do you still want to let it access the internet? Path C:\Program Files\Microsoft Office\Office11\Outlook.exe."

Below that is a box stating "McAfee does not recognise this application." with a hyperlink "Tell McAfee about this program" which takes you to a reporting page at McAfee's website. At the bottom are two options - "Grant Access" and "Block All Access". I select Grant Access to carry on but keep being prompted with the same message every time Outlook tries to send or receive email. This becomes increasingly annoying. I have not changed anything in Outlook and the problem is not there every time I switch the PC on, only now and again.

Is there any way I can get McAfee to allow internet access to Outlook so that it doesn't ask me every time?