Recently, while upgrading the firmware on a Pro 3060, from 4.2.0.0 to 4.2.1.0, I received the error message “Firmware too large for this device”.  After a short bit of research, I found that when receiving this error message, you must boot into Safe Mode, then upload the firmware there.  Be sure to back up beforehand!

http://www.fuzeqna.com/sonicwallkb/consumer/kbdetail.asp?kbid=7618