I have a PIX515E which used to allow me to successfully connect to a client's VPN using Windows XP PPTP. I'm connecting successfully but the login/password stage is hanging. I've spent a couple of days on the issue and implemented various ideas including
conduit permit gre any any
conduit permit tcp host [ip] eq 1723
static(dmz,outside) [outsideIP] [dmzIP] netmask 255.255.255.255 0 0
Also I've added:
fixup protocol pptp 1723
although I've read that my version of the firmware (6.3(1)) has a bug which was fixed in a subsequent upgrade.
tnx for any advice