Will DYN DNS affect VPN access?

I use Dynamic DNS for a dial up account. I recently upgraded to 4.1 and have been unable to establish a VPN connection. I have satisfied all parameters in the manual concerning remote access. I have tried ip addresses and domain names to connect with my e-smith. I have pinged my WWW. name to resolve the IP and this address does not work. The most successful "failure" leaves a Windows error: 751 " The remote computer refused the VPN connection. Please try again latter. If this problem persists, check with your network admin." Any body have an ideas what is going on? Thanks Steven Lewis