I would like to create a script to alert and prevent errors when amount A is greater than amount B. If possible, the script will not allow user to proceed without making the necessary correction to amount A.

How can I do this ?

Why creating a script, that you must fire ?

Isn't better to create a field (autoenter) with some type of validation (and a custom message too) ?

for example:

validatingField:

autoenter calc = amountB - amountA

validation by calc = amountA ≤ amountB

Thanks Raybaudi for the suuggestion. Must admitt that I did not think about going to a validating field. It works just fine.