This is a very short and sweet one. Clear your variables. Trust me, it is worth it. It’s easy and will save you time debugging.

To clear a variable just do:

vVariable=;

Also if you tend to copy apps as starting points, don’t forget to delete old variables. The above used to actually remove the variable from the app. However, this is no longer the case. To remove the variables, you will need to go into the variable overview on the Analysis page’s edit screen.

Documentation.