On this AP is 10 users conect. Minipci R52H ,Polarisation Vertical, B standard ,antena is Sector 14db 120H/30V, This problem hapend couple of day. Users use Yagi and grid antenas.
you sector antenna is horizontal polarity, be sure that, all the client site is in the horizontal as well...
I would suggest you do not use the yagi antenna due to it's circular wave, couple it with the sector antenna that's not the good idea.
one more thing, even you sector antenna is 120 degree, but the better coverage should within 90 degree.
hope this help.