You seem to be doing a lot of guessing and no reading of documentation on the TextBox control.
You cannot just name a function to what you want it to do and expect it to work. You have to work with the events you're given by the control, and that stuff is covered in the documentation on it.
What you're trying to do goes against how a Windows application is expected to behave. Enter usually submits an entire form and Tag navigates between fields on a form. Why is this? Accessibility reasons.
For you to do what you want, you'd have to handle the
KeyDown event[
^] of the textbox and look for the Enter key being pressed. If it's pressed, you can call whatever method you want to handle what happens in that situation.