After I posted my help request I remembered Chris de Herrera's website
www.pocketpcfaq.com. His advice to go into activsync options and uncheck all the applications, adding them back in one by one so as to isolate the offending application.
What happened was that I got pushed into an activesync setup screen which showed that I had two connections set up with the same name and details. When I deleted one of the connections the problem was sorted. I can now sync.
I don't know how two connections got set up.
Thank to everyone who responded.
Jim