According to this Microsoft Knowledge Base entry, there are registry entries for PPTP in SP2 that you may need to set or update. Microsoft and others have noted that Windows XP SP2 introduced problems for VPNs, such as L2TP/IPsec, that require NAT traversal (NAT-T). While these problems shouldn't affect PPTP, PPTP is very insecure and you should consider upgrading to L2TP/IPsec if you have anything greater than casual security requirements....
If you do decide to upgrade, see this Knowledge Base article for information on fixing the NAT-T problem.
Visit our Learning Guide for Windows VPN troubleshooting tips.
Dig Deeper on Virtual Private Network (VPN)
Related Q&A from Retired Expert - Jon Snader
Learn how to set an IP address on the network interface of a FTP/Web/mail server when a client has only one public IP address.continue reading
To connect to a WAN remotely, your client can use a VPN client or a leased line. Learn the pros and cons of WAN connectivity with each option, such ...continue reading
When using ISA 2000, some users can lose connection to the network and experience packet loss even if the VPN client is still connected. Learn how ...continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.