Off and On VPN

My boss is really on my case about this issue and I'm at a loss as to the
cause. Have a Windows 2003 domain with roaming profiles that use a Firebox
X1000 as the firewall. Set up VPN through the firebox and 50 of the 52 users
connect just fine. My boss happens to be one of the ones that is having
problems. He has Windows XP Pro and went through the Wizard to create a VPN
connection. It will work sometimes and other times it doesn't. It does this
on all three of his home machines. He sometimes gets error 721 when trying
to connect, he'll leave it come back 15 minutes later and it will connect.
Other times it will just time out. I'm baffled, any help?