I have a problem with the CN2 power input

I'm using the CN2 pin to control the Power Latte Panda using another Arduino. however when I use the 5V input on the CN2 pin, the blue LED flashes like a wavy and the red LED flashes quickly and then turns off. however, if I use the same adapter and use the micro usb port, my Latte Panda works fine. where is the problem? anyone can help me?