VBA Macro To Move Shape Around Spreadsheet

I am trying to write a set of code, part of which involves moving a shape around an excel spreadsheet in a square shape within a certain range. It is based on a random number generator. The shape moves a number of cells to the left/right/up/down depending on the random number (d) multiplied by 16. If the shape reaches a row or column border point, it will change direction but continue moving in the new direction until it has gone as far as was determined by the random number (*16). I have some code which works fine... to a point! The shape starts out, reaches a right hand border, changes direction to go up, reaches another border, changes again and goes left, but then when it comes to change dorection the 3rd time and go down, it fails. The direction of the shape is determined by a word in cell A1 - left/right/up/down:


Sub MoveRed()
Application. ScreenUpdating = True
Dim d As Integer
Dim i As Integer

d = Range("AZ1").Value

With ActiveSheet.Shapes("RedDot")
For i = 1 To 16 * d

Select Case Range("A1").Value
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