I got no replies from anyone :-(
In the end I gave up with the VPN client on FC4, simply could not get it working reliably. However, for my project I backed out to FC3 and all the VPN problems went away. My conclusion - there is a binary incompatibility with the Cisco binaries, compiled with gcc 3.95 and the libraries on FC4 compiled with gcc4.0
I had no intention of keeping any answers to myself. I am a great believer in 'the common knowledge'. I was anticipating having to send debug files etc and posting such things to a group isn't a good idea. Had I got to the bottom of the problem with help from someone in this group, I would have posted a summary of activity.