If you dont wipe cache from going to RC2 to RC3 you might have this problem. I have now the market sice i wiped the cache. Dont worry guys..market will install your apps. good luck.
I installed CM6 rc3, including google apps, directly over Sapphire 1.0.0. I did not wipe/erase cache and have had no significant problems. Market automatically installed almost all my apps but I did have to manually uninstall and, then, re-install a couple of apps.
Running very smoothly. Doing a complete system/boot/cache/etc. deletion via ROM Manager. Hopefully, that will help.