I just received this email. it may help!
I have been recieving quite a few emails and PM in regards to units locking up after or during the update and wanted to post this for everyone again.
All or at least all of the problems I have heard about during updates have been when users have inserted the SD card prior to Powering on the Unit. I have this problem on my 997c, it will not take an update if I put the SD card in first.
The Official Humminbird Website says to Power On the Unit, then Insert the SD Card!
http://www.humminbird.com/support/FAQ.aspx?faqid=35
After you have Restored the Factory Defaults, just insert the SD card and the unit will begin the update. You can power it down and back on again if you want, but wait until it is completely booted up before sticking the SD card in the slot.
A lot of older material says to insert the SD card before you power on. This will work with most units, but I highly recommend you do not use this method! This is how the original updates were done, and it was later changed.
Robert