Procedural database execution of gimp-image-convert-grayscale failed

["loicprojet" <loicprojet@xxxxxxxx>]

Hello,

I have this ERROR message since I install Gimp 2.4.0
Procedural database execution of gimp-image-convert-grayscale failed

My script-fu is quite simple but I can't understand where is the
mistake. Just have look. Thank a lot for your suggestions

(define (script-fu-bb image drawable location inText)

 (let*
	(
	(theImageHeight)
	(theImageWidth)
	(theOffsetX)
	(namepng)
	(layer)
	)
	(gimp-image-convert-grayscale image) 0

	(set!	drawable	(car	(gimp-image-get-active-drawable image) ) )
	(gimp-by-color-select drawable '(255 255 255) 60 2 1 0 0 0)
	(gimp-edit-cut drawable)

	(set!	theImageWidth	(car	(	gimp-drawable-width  drawable) ) )
	(set!	theImageHeight	(car	(	gimp-drawable-height  drawable) ) )

	(set!	theImageWidth	(/ (* 180 theImageWidth) theImageHeight))
	(gimp-image-scale image theImageWidth 180)

	(set!	theOffsetX	(/ (- 240 theImageWidth) 2))
	(gimp-image-resize image 240 180 theOffsetX 0)
	(set!	layer	(car	(gimp-image-get-active-layer image) ) )
	(gimp-layer-resize-to-image-size layer)

	(set!	namepng	(string-append location inText ".png"))
	(file-png-save2 1 image drawable namepng inText 1 2 0 0 0 1 1 0 0)
	(gimp-image-clean-all image)
	)
)


(script-fu-register "script-fu-bb"
	"bb"
	"creation format illustration"
	"Loic"
	"copyright 2007, Loic"
	"Mars 2007"
	""
	
	SF-IMAGE	"Image"		0
	SF-DRAWABLE	"drawable"	0
        SF-STRING   "location"      "Desktop/Images/"
	SF-STRING	"Text"		"a"
)

(script-fu-menu-register "script-fu-bb" "<Image>/Script-Fu")