Please help. Having a lot of trouble un-rooting

Okay, I've been trying to unroot my droid (so i can sell it) all evening. I tried rom manager...error messages every time. I tried RSD Lite....error message.

I finally was able to get somewhere with SPRecovery with update.zip in root of SD card...but when i rebooted phone, i get FCs. For example, "The process android.process.acore has stopped unexpectedly. Please try again."

What do I need to do to get this to work appropriately? All I have is notification bar and a black screen. I really need to get this working tonight with most recent 2.1 (stock) so i can mail it.
Thanks!
Tommy

For everyone who has helped me tonight: thank you. I have no clue what got into this phone...but geesh...it was crazy. I finally was able to get it unrooted with 2.1.

got it as i was posting a link....... sorry i was too slow