I have same issue here...i did the SBF update on my Droid 2 using RSDlite and an original stock ROM. After this I placed the newest Gingerbread "update.zip" in my sd card's root and did the stock recovery mode (power + x) (then hit the magnifying glass) and when i tried to update it it ran but it failed saying this below:
"E:Can't open /cache/recovery/command
--Install from sdcard...
Finding update package...
verifying update package...
E:Failed to open /sdcard/update.zip
(No such file or directory)
E:signature verification failed
Installation aborted."