WZR-G300N Wireless G Card Issue

Try setting the following in the router's web interface under Advanced-> Wireless Config-> Basic:

1. Set Channel Bonding to 20MHz from 40MHz.
2. Set the Control Sideband to Lower.
3. Enable 802.11N Protection.
   

If these do not help, try updating the latest firmware for the device at:

http://www.buffalotech.com/support/downloads/
* Select Wireless-N Broadband Router and Access Point ->firmware.