Hi.
I'm surprised that you ever got it working on a Windows 2003 server, as it only supports the following (taken directly from the installation guide for VPN client 4.6):
Verify that your computer meets these requirements:
?A single, Pentium?-class processor.
?One of the following operating systems:
?Microsoft?Windows? 98, or Windows 98 (second edition)
?Windows ME
?Windows NT 4.0 (with Service Pack 6, or higher)
?Windows 2000
?Windows XP
http://www.cisco.com/univercd/cc/td/doc/product/vpn/client/4_6/ugwin/vc2.htm
-Joe