I am unable to connect to Mikrotik RB751G-2HnD with LG smart Phone P-700, if the wireless connection is encrypted,
I tried wit WPA only , WPA2 only, AES + TKIP, TKIP only, AES only, etc... without success. LG phone is able to connect
only to open wireless network. Does anyone have similar issue and know how to solve the problem.

1. Have you setup the security profile and associate it with the AP correct?
2. In the setup with security (not open network) can you connect with other wireless devices (phone, laptop, tablet)?

Regards,

I did create correctly security profile, I am able to connect over encrypted network with any device, except my LG Smart Phone. I am able to see the LG phone trying to connect, but after 4s the connection is dropped and it's dropping constantly, the phone never gets an IP, there is no problem with other wifi devices.

contact support@mikrotik.com to get v5.22rc1 for testing.
Also remove the AP profile from the phone after you upgrade to that version and setup for using WPA2.

V5.22rc1 solved my problem.