I have connected my Win XP laptop with cable directly to the router, and I am trying to update firmware to version 1.45.10 which should be the correct update for my model, but the upgrade is interrupted with "Upgrade file pattern error".
I have tried hard-resetting the router before upgrading, but with the same result.
How are you upgrading the routers firmware? Are you using the router web-based user-interface? If you are then try using this alternate way...
Go to www.linksys.com/downloads .. search for BEFW11S4 v3 ... then download the Set-up Wizard. Use this to upgrade your router instead. When you run this program, it will ask you for a server, password and then a file. Server is the router IP, password is the router password (default is admin) and file would be the firwmware you downloaded... once you input the necessary info... hit upgrade and you should be good to go.
you were right in the assumption: I was using the web-based router interface for upgrading. And your suggestion worked: when I used the set-up wizard there was no problem in upgrading. So thanks a lot!