It doesn't look like you're overlooking anything.
My only recommendation, maybe, would be to rename the file to
"update.zip" before copying it to the SD card... (8+3 filenames vs
long filenames).
If that doesn't work, you may want to try reformatting your SD card -
I have a vague memory of some cards coming out of the factory
formatted in a way that recovery didn't recognize, but I didn't think
that this made it into production for the ADP1.
JBQ
--
Jean-Baptiste M. "JBQ" Queru
Android Engineer, Google.
Questions sent directly to me that have no reason for being private
will likely get ignored or forwarded to a public forum with no further
warning.