Hi!
I also had the same problem before with my WPC54G. I tried to uninstall netstumbler and it didn't work!

but then, I tried to search the web and this is what I found...
http://www.mnetweb.co.uk/linksys
I followed exactly what is indicated here and it worked!!!
I can't use netstumbler though...
Hope this site will help you.
