Help! This code isn't working"

Hi! Im new here. Im from Brasil, so my english may be bad.

Im working in a code for a form. In this code, the user need to enter 2 variables : "Grupo" (a 6 numbers data) and "Cota" (a 3 numbers data). After that, the code need to check in the worsheet if this specific combination of grupo and cota (let's call this the g/c) hasn't been imputed yet. If this specific g/c exists in the workcheet, i whant the user to see a msg called "Já_Existe", if this g/c dosn't exist in the worksheet i need the code to imput this new data.
Take a look in what i have here:

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If the especifi g/c exist, all comes out great, the user can see a msg saying that there already exist this g/c, but, when a new g/c is inserted, all my excel crash down. What im i doing wrong??