I have a textbox on a user form that is giving me an error when a
number is entered in. This number is a percent and the code for the
textbox is:

Private Sub TextBox35_AfterUpdate()
If IsNumeric(Me.TextBox35.Value) Then
Me.TextBox35.Value = Format(CDbl(TextBox35) / 100, "0.00%")
End If
End Sub

This works fine only if I enter a whole number(?), meaning, 10, 12, 30,
44 all will work. But if I enter 10.3, then I get the error. Any
thoughts on where I'm going wrong?

There is another button on the form that when clicked will mulitply
textbox1 x textbox35 + textbox1. So the flow is: 1) a value is in
textbox1, 2) I enter in a 'markup', say 10.5 and click the button. The
error comes up at that point, again, only if I use a '.'....in
textbox35.