I have built a User Form that asks for an employee ID number to be entered.
That data then goes to cell A2 on the spreadsheet. Cell A1 has a VLOOKUP
formula that goes to another sheet and finds that employee ID number and
returns the name to cell A1. If it can't find the ID number then #N/A
returns in cell A1.
I want to create a message box that will pop up after the user types an
invalid number in the User Form indicating "Invalid Employee Number".

How can I do that? Also, I know this sound s extremely simple, but being
new to this I am unsure. The code for the above message box, where do I
insert that? I assume in the code for the User Form?

Thanks so much for any assistance!
Tim