Hi guys, quick response, really impressed.
Matt, No I didn't have Super Cache on when you had a look, sorry. I realise that that would have helped with diagnostics but was loathe to leave the site in a "non-working" state.
donncha, After logging out of everything last night and re-logging in today, I immediately activated Super Cache and set it to caching on. I then went to the Advanced tab and set evrything to "recommended". I noticed that the mod rewrite rule was flagged as an issue. I clicked on the "Update mod rewrite rules" and the process went through. Both Super Cache and Shadowbox are now activated and running together. However I now have the problem of "timestamps differ or not found" warning when the test cache is ran. Not sure if this means Super Cache is working effectively or not. I have left both Super Cache and Shadowbox activated and will from now on.
Thank you both for your quick pro-active response.
Best Wishes
John Chadwick
John-Chadwick.com