Windows firewall and VPN

Set up a VPN using the standard Windows client (using the wizard) to my
office network. Having been using this for months successfully (but haven't
used for about a month). Has stopped working properly. I suspect due to
updates I applied at some stage over the last month. If I turn off Windows
Firewall it works okay.

To clarify "not working properly". It connect okay, but I cannot access any
of the shared folders. I cannot even ping the server. If I turn off Windows
Firewall it works fine.

What exceptions do I need to include in the Windows Firewall for it to let
the connection through? I have tried unchecking the box next to the
connection in question (on the advanced tab), but that didn't work. Only
completely disabling the firewall.