When i see clients here in my WLAN associatte & disaccoiatte quickly it usualy turns out to be an authentication setting on the client is incorrect.
The first 'connection' you see is the client & the AP negotiating an association.
it fails - client dc's - lather, rinse, repeat.
Check your settings -
I recommend Socketcom's WiFi companion, byt a freeware - WiFiFoFum - is highly respected as well...