cannot get context.imagedata using vb script (not javascript)

I have the following code in my page and it keeps conking out at the line where I try GETIMAGEDATA

<script type="text/vbscript" id="PreviewRangeFromPalette">
Function PreviewRangeFromPalette(evt)
	Dim oMouseX 
	Dim oMouseY 
	Dim oCanvas1
	Dim oContext1
	Dim oImageData 
	Dim oDataRect
	Dim X, R, G, B, A
		oMouseX = parseInt(evt.offsetX)
		oMouseY = parseInt(evt.offsetY)
		UpdateMouseLocation oMouseX, oMouseY
		Set oCanvas1 = document.getElementById("ColorPaletteImage")
		Set oContext1 = oCanvas1.getContext("2d")
		Set oImageData = oContext1.GetImageData(0, 0, oCanvas1.width-1, oCanvas1.height-1)
		'msgbox(oImageData.height) OK - This returns the correct height
		'msgbox(oImageData.width) OK - This returns the correct width 
		oDataRect = oImageData.Data
		'X = ((oMouseY * oCanvas1.width) + oMouseX) * 4
		'R = oDataRect.data(X)
		'G = oDataRect.data(X + 1)
		'B = oDataRect.data(X + 2)
		'A = oDataRect.data(X + 3)
		'window.document.getElementById("PreviewColor").style.BackgroundColor = "#" & Hex(R) & Hex(G) & Hex(B)
		Set oCanvas1 = Nothing
		Set oContext1 = Nothing
		Set oImagedata = Nothing
		'Set oDataRect = Nothing
	End Function</script>

The HTML I used is

<canvas id="ColorPaletteImage" height="256px" width="256px" style="width: 256px; height: 256px;" onmousemove="PreviewRangeFromPalette(event)"><noscript>
								Your browser does not support the HTML5 canvas object!</noscript></canvas>					

Why does it conk out on the getimagedata statement?

I receive the following error

Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/6.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)
Timestamp: Thu, 23 May 2013 00:06:38 UTC

Message: Could not complete the operation due to error 800a01bd.
Line: 181
Char: 1
Code: 0
URI: http://localhost:56248/EShopAdmin/SelectColor?OId=300&CId='n%2Fa'

Please can someone point me in the correct direction to resolve this using VBSCRIPT

DocZaf