After I installed the ICS zip update to my rooted Razr Maxx on .181 GB my WIFI Tether stopped working with the same ad hoc error message. For some reason I can not get FoxFi to work either.However this:
How to Get Free 4G LTE Wifi Tether/Mobile Hotspot on Rooted Droid Razr! | DroidRazrRoot.com worked for me. Note that some people have said that the "Entitlement" is now on line 79 but it was still on line 150 for me. When I turn wifi hotspot on I don't get the prompt from Verizon. My lap top finds it right away but it sometimes takes a minute (literally) to make the internet connection.
I really liked wifi tether and expect that there will be a work around soon. Until then, this works for me.