I am getting the "unexpected error" also.
I am running a HTC HD2 TMOUS, 21XX ROM. I access the google.com/voice/m/sms page via IE and it's fine... anyone know what the problem is / what is the fix?
Also I should mention, iDial only works AT ALL if I first LOG OUT of my google voice on IE. If I am already signed-in and the cookie has me to "Stay signed in", the iDial doesn't work at all (the login dialogue never shows). So the procedure I've been using is to log out of google voice on IE, then use iDial, type in my login, then receive error.