base stations appear on iphone and iPad, but not on macbook

hi everyone

i am struggling with my aiport utility on my macbook air not showing base station(s).

i have mountain lion 10.8.2 and use airport utility 6.1.

my time capsule (802.11n) is connected to my router, one airport express(802.11n first generation) is added for airplay and one airport express(802.11n second generation) to enhance wi-fi on the second floor.

everything works just fine...

BUT... my base stations will not show up on my airport utility on my macbook (base station cannot be found...). the airport utility app on my iphone 4 and iPad 2 show all the base stations perfectly.

what is different on my macbook? i have downloaded the airport utility 5.6.1 as well because of the problems with 6.1 on mountain lion. but it's the same thing on both airport utilities.

thanks for your input.