Hi Stefan
Many thanks for all your help, the problem is resolved, I had changed several sections to add extra feedbacks and had mistakenly added the same feedback number to 2 bits track, as 1 of them was not connected to a module it did not show the section as occupied but the computer saw it.
I am away to modify my diagram to take into account all the information you have given me. It is good to learn. I am just thinking of upgrading to the latest version as James informs me it is a lot better.
Many Thanks
Chris