From a Google search, I find that there different programs/products named Grabit … and even different versions of such things. So, a little more info about the Grabit you have would be helpful.
I never use those IM things so I can’t be of much help here except that there must be some place in the MSN Messenger program to specify this if the service requires it. I would guess that anything downloaded from the internet would be covered either by the Web Shield or the IM Shield. The latter has a checkbox for MSN Messenger but I do not know if this covers the beta version you have. If you have not yet marked that check box, then you could try and see if that solves it.
Left click the “a” ball in the task tray > scroll to top of left pane > click on IM > click on Customize > mark the top check box for MSN/Windows Messenger
I do not even use those things but I have all of those boxes checkmarked just in case I forget (old age creeping up on me and such) why I stopped using those things … plus this is not too much work load for my system.