NaN errors can be encountered in virtually every software application (pun intended). However, unless you understand what NaN means, this error message is less than helpful.
NaN literally means Not-a-Number. Now, wouldn't that have been easier to understand? Not A Number designates a non-numeric or invalid numeric response. A value that is undefined or unrepresentable. An example is zero divided by zero ( 0 / 0 ) where each character is legitimate on its own, but this numeric transaction is not valid. So, let me break this down in non computer programmer language.
NaN as an error message may also be accompanied by 'Unquoted literal constant'. (Also fairly meaningless unless you know what those words mean when used together.) NaN is an acronym, shorthand if you will. Since NaN always compares unequal to any number, NaN is generally used to indicate an error condition for a function that should return a valid number.
That still sounds a little like brainiac talk. When you are entering data, sometimes alpha responses are required and sometimes numeric responses are required. Even if numeric responses are required, and you enter a numeric response, you could still see this error message if the value is not legitimate. For example, when entering dates. If you want to indicate November 13, 2020 but you enter 111/13/2020 or 13/111/2020 by mistake, you may well trigger a NaN error. Likewise, if you are asked to populate a full 24 hour period, say when creating a default Pitch Schedule Template, and you inadvertently neglect to account for all 24 hours, when you try to save your work, you may well see the NaN error message.
Hopefully, this provides some clarity and an understandable explanation.