Hi all together,
I have to solve the same problem. Unfortunally I can't use the solution "controlled upgrade" because we use at about 20 AP3805 in a warehouse environment.
I tried to upgrade the AP manually via tftp and received the following message:
##########
image_upgrade
TFTP Filename in progress....
TFTP done.
core enabled
Error! Image file header not found!
No core files while upgrading
/usr/sbin/image_upgrade1: Clean up and exit with return value 12
############
I extracted the AP_FW-file from AC-MV-09.21.09.0004-1.bge as described by Gareth and Andre.
Yes I resetted the AP as described by Umut with cset f.
Is there a solution for manual upgrade/downgrade of the AP?
Regards
MIchael