I am building model following the exercise given in the manual, with base year 2010. I get this error message for 2011 (please see the attachment), could you please explain me what does it mean and how to get rid of it.

This may be a temporary glitch in LEAP's user interface. In these situations, please just restart LEAP. If in fact you did enter an empty expression, then the solution is don't! Expressions must contain a valid number or mathematical expression.

PS If you are sending a screenshot, please attach JPG or similar images rather than Excel files. They are much easier to see!

Hope this helps!

Charlie