Hey mcm,
I have a A570IS as well but I haven't been able to find software to correctly a) read the CRW files and b) convert the CRW files into working DNG files. This is all being done on my mac and I've tried countless options...automator actions, PS CS3, Lightroom, random software - you name it.
However, when I took the CRW files to XP, I was able to use that DNG4PS-2 software and it converted it without any problems to DNG files. I was then able to take those files back over to my mac and work with them in Photoshop.
I'm not sure if you work on PC or MAC but do you or anybody know if there is working mac software to successfully convert the CRW files into DNG files? It would very much save the hassle of switching between XP and MAC everytime >.<
With regards to your question; I haven't processed DNG files on lightroom so I haven't experienced the issues you're facing. Do artifacts always appear in the DNG files and it is simply lightroom that can't seem to remove it? Not sure how to resolve this one.
HV