Yes there is a message and when you click ok the program stops. Don't you instead of the blunt message redirecting the user to a question to reset the correct path would be more efficient? I don't know I have developed rather complex programs for financial analysis and such situation was always tested in my programs. And mind you I'm not a software developer by profession. I was primarily a financial analyst but in 1972 I realized all the possibilities programming could bring to my job. I first used Fortran IV an then APL+ a fantastic language based on the principals of modern algebra and Matrix operations. It was invented by Kenneth Iverson a professor at Harvard. If you're interested read this page by Eric Lescasse. Eric made me discover the language and taught it to me. A fantastic guy. he told me he used the language to make a simulation of the traffic of LAX airport for his thesis at the end of his college years. http://www.lescasse.com/lc/APLHistory.asp .He owns his company . So you see I do not talk in theory.