I am downgrading a PIX Firewall from 7.0 to 6.3. I faced probelm when rebooting the PIX.
The error shown as below,
Booting first image in flash
Image must be at least 7-0-0-0 error in file flash:/pix635.bin
No bootable image in flash. Please download an image from a network server
in the monitor mode
CISCO SYSTEMS PIX FIREWALL
Embedded BIOS Version 4.3.207 01/02/02 16:12:22.73
Compiled by morlee
128 MB RAM
Did you follow the exact downgrade procedure shown on this link.. did you point the 6.3.x image as indicated
pix downgrade procedure from 7.x to 6.3.x
in any case, you can still redownload the 6.3.5 code again from monitor mode.
let us know how it works out.