I have a new Sanyo Z1 projector which is a couple of months old. On dark images - or when the "no show" button is pressed, a circular blob of slightly lighter area (with a greenish tint) is visible on the screen. This is static and about 5 inches in diameter - the screen is 6 foot in width. (located to right of screen about 1/3 of distance from bottom. The appearance of this has occurred subsequent to initial use. Can anyone explain what might be causing this.