A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
Your grades routine refers to Textbox35 and higher but they do not exist on your form.
By the way, a lot of your declarations are wrong. If you write:
Dim rng1, rng2 as Range
only rng2 is declared as a Range object; rng1 is a Variant. You have to specify the type for each variable individually.