VB Code:
  1. If IsError(Text1.Text / Text2.Text) = True Then
  2.         MsgBox "Error"
  3.     End If
Is not the correct way of using the function. it
will generate a Runtime error 424. The function is suppossed to be used like...

If IsError(expression) Then...

The required expression argument must be a Variant of VarType vbError.



Why not just check for the text2.text being one character and it
being a zero. if it is a negative number that would be ok.
VB Code:
  1. Private Sub Command1_Click()
  2.     If len(text2.text)=1 and instr(1,text2.text,"0")=1 Then
  3.         MsgBox "Divide by zero error"
  4.         text2.text = ""
  5.     Else
  6.         text3.text = Text1.Text / Text2.Text
  7.     End If
  8. End Sub