thanks for your response. Just as a matter of curiosity why is such an error not trapped and explained? In all the apps I have written over the last 35 years,including at least two complete 2D modelling systems which have similarities to this one, I have always included error trapping, associated messages and pointed to somewhere in a manual to help the user sort things out. I do feel Telemac front end needs an update!! Anyway here is the cas file - if you can spot something that would be great thanks.
George M