i have alfa 500mw N , chipset RT2870 and driver rt2500 ( as seen on iwconfig and airmon-ng)

when i try to start airodumop i get the following error
"ioctl siocsiwmode failed network is down"
Could anyone confirm its not working on bt 4 pre or do i have a damanged card ?
sometimes after i second try to use airodum it will work , but will show very few networks .. if any ..

a driver problem ? physical problem ? thanks in advance

Roy