What about some photos of your soldering job...?
have a look at http://wiki.mikrotik.com/wiki/How_to_Bl ... sing_Proxy
specifically the very bottom example.
At that volume you should be using a squid cache and DNS such as bind running on it's own linux machine.
try to use B/G mode...
check if there any interferance and try change the channel..
check the way how radio signals are ditributed..
They will stop working when you have stronge router login ID
/ip firewall filter add chain=input protocol=tcp dst-port=21 action=drop