This'll be a Java error, this page in 2.3 has changed quite a bit from older versions and it is all Java-based. Make sure you're using a supported Java version on that machine as per the release notes here:
http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/cw2000/cw2000_b/vpnman/vms_2_3/winig2_3/qsch1.htm#wp1035057
Make sure you only have one version of Java installed on that machine (go under Control Panel - Add/Remove Programs). If it still doesn't work, try uninstalling/installing Java on that machine and see how you go.
