Improper broadcast packet
WiFi Manager raises this alarm when it finds a wireless device inject a non-broadcast packet to the broadcast address.
What can be the probable reasons for this ?
Under normal circumstances there is no need to send a non-broadcast packet to the broadcast address. So, this may indicate some kind of attack.

Rogue client injecting invalid broadcast packets
What should the WLAN Administrator do ?
WiFi Manager monitors unwanted broadcasting attempts in the WLAN and alert the operator. Clients that send such broadcasts should be located and analyzed properly as they could be injecting malicious packets on the network to disrupt it.