You appear to be creating an image which is 0 pixels wide and 0 pixels tall, as GraphicsHeight and GraphicsWidth are undefined. If you meant to use the inbuilt functions, you have to use parentheses to get return values.
EG, this:
needs to be this :
EG, this:
Global width=GraphicsWidth:height=GraphicsHeight
needs to be this :
Global width=GraphicsWidth():height=GraphicsHeight()