need fast help 5d ii (exposure comp dial)

HI all,

I've had my 5d2 for about 2 weeks. I upgraded from my 40d. i'm shooting in Av mode. the thumb dial is not adjusting my exposure compensation. nothing changes when i turn the nob. i can go into the menu setting and adjust the exposure comp but i don't want too.

my thumb dial worked yesterday for exopsure comp... my thumb dial works for all other settings and functions. did i turn something off or on? my daughter's bday party is about to start and i can't find out what's up by going through my manual.

thanks for a quick note.

craig