Canvas.toDataURL() throws security exception

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Javascript

HTML5

Hi!
I've a html page that has a canvas on it. I'm trying to convert canvas to image. Actually it works when its on local IIS server.
However , it doesnt work when i run it as a independent hmtl file. When i debugged it on google chrome i get following exception.

Line:

var strData = oScaledCanvas.toDataURL("image/png")

Exception : Uncaught Error: SECURITY_ERR: DOM Exception 18

I guess, canvas has some security restrictions.
My question is , how can avoid this exception ?
Or how can i convert canvas on local html file to image ?