IF(ISERROR(AND ($AN="ii", $Cn="b")),"there is an error",IF (AND ($AN="ii", $Cn="b"), formula- $En, formula))

where N is a number and n is another. ii & b are conditions that mean something. Usually errors are caused by empty cells and arithmetic. Or those numbers exceeding the limits (negative or >65,000). Which could be trapped but it gets pretty complex IMNSHO.

well that's how I would do it, or more likely write a macro "Function", declare it in a "Module" and use it in a cell. Are you still following me?

macros can be recorded and used by setting up a button but once you start conditional logic it becomes a programming exercise, you have to need the result to go that route.

Now if you click on the "fx" text in the formula bar you get a dialog that you can search for functions in categories. Doing it to a formula will help you work out elements in the formula. Highlighting a part can help on just the part. I still have to scan to get the function I want, it is logical, but not in my head necessarily.

Best of luck. Feel free to PM me - I may be able to highlight something.