Wifi connection might drop spontaneously or simply cannot connect. Users on Ubuntu 10.04 and 11.04 have reported experiencing the problem.

Running dmesg would show:

[210749.637705] wlan0: deauthenticating from 00:23:89:48:3b:b0 by local choice (reason=3)
[210778.632244] wlan0: deauthenticating from 00:23:89:48:3b:b0 by local choice (reason=3)
[210784.456359] wlan0: deauthenticating from 00:23:89:82:75:70 by local choice (reason=3)

which is pretty cryptic.

I have tried: kill -9 wpa_supplicant, but wpa_supplicant keeps getting restarted each time.

Also, some have suggested that this was caused by enabling power management. However, this might not be true, as the problem has presented itself in a situation where power management was disabled.