Mikrotik problem

[CALINJOS]

ISPRICAVAM SE STO JE NA EN ALI SAM BIO TO ORIGINALNO NAPISAO NA EN PA MI SE NIJE DALO PREVODITI
I use MikrotikOS 2.9 for my wireless network as central point. It has 2 wlan cards i 1 ether. Mikrotik is set to be just a AP (2 AP's to be exact) and bridge between these 3 interfaces.
Problem is that when I try to copy some thing from another computer which is connected over wireless, connection brakes down at middle of coping. First I thought that wireless connection with that client brakes down but then I realized that I lost connection with ONLY that computer.
For example there is client (AP in client mod) connected to Mikrotik with few computers on switch in his own network and when I lose connection with one of them while trying to copy it is ONLY with that computer from which I tried to copy, other from that network I can see and access with no problems.
It's like Mikrotik block access only to that IP. When I try pinging that computer I got 100% lost packet but that block is only for me because others in network at the same time can see that computer and access him. After that I have to wait for few minutes to access that computer again. This phantom problem occur not only to me but to everyone in network who try to copy some thing and traffic goes through Mikrotik.

Sorry for amount of text but it's hard to explain what happens in just few words.