This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
The error means that the variable can not be found in your code. You don't have these variables defined in your code: mexicoPopFin, usPop, mexicoPop and the Years variable is only available inside the if statement where it was declared.