Halfred and JF-
i've also been playing with those same scripts. My discoveries so far:
1) Most require the layer to be RGB or RGBA.
2) Most require the layer to be worked on to be active AND select all
3) Almost all of them will fail if the active layer (the one targeted for the function) is layer size = image size.
I have discovered that changing the canvas size to be +100 x +100 (as in 100 px added to each dimesion) and then running the script, allows the scripts to function. Most of them work great out of the box, but fail miserably if that size difference isn't there.