[BritSteve]

Finally located the problem. In my case a smarty template was being compiled into invalid code. If you check the xcart logs, you can see which compiled template has the problem. Deleting the compiled template forces a recompile, but the template will still have the error. I edited the compiled template and corrected the error, and everything works now.

I guess that Smarty has a bug in the compiler that produces invalid php code, even though the code in the template is correct. In my case the compiled template had a missing quote.

Hope this helps others who are experiencing this problem, sure is easier to fix than restoring from backup!

Steve