Windows VPN problems after update

Win XP Pro SP3
After the update slisted below, 2 of my users cannot maintain a VPN
connection back to the office for more that one hour (sometimes as little as
5 minutes).
They are 2 different laptops from 2 different locations. I have even tested
them on a test broadband connection with the same results.
It seems like the VPN (windows PPTP) connects to our Win 2003 Server STD and
they can open outlook. After a while (as stated above) outlook flags up that
it cannot access the exchange server but the VPN connection (icon) still
appears to be connected (although no data is received).

Has anyone else had similar problems?

Updates:
KB975467
KB973525
KB971486
KB953297
KB974571
KB974455
KB975025
KB974112
KB954155
KB969059
KB890830
KB958869
KB974417