Ok, the remedy: Thye problem I had was to do with file ownership. There are several threads to do with phpsuexec on Surmunity here To cut a very long story short, if re-upload module files and update the module, correct ownership is established and the module will work OK. I have done this and my forms are now ok.

There are lots more details to the why and how, but I suggest you check out those threads on surmunity.

Thanks for your comments Herko and Martyboy.