I have never seen that message before.
I just found out the other day that PHD2 has manual dithering
see here:
http://www.iceinspace.com.au/forum/s...d.php?t=117669
but your version PHD1 doesn't so I can't understand how you are obtaining dithering -
it sounds like it's through Nebulosity.
Therefore it might be a bug in Nebulosity.
Maybe download PHD2 & try to manually dither?
Maybe reload Nebulosity?