A client recently installed a Pentair ScreenLogic2 system to control their fountain. It was having an issue where the Ethernet cable tested fine, and connecting a laptop pulled a DHCP address.  When the cable was plugged into the protocol adapter the link lights would remain dark on both the switch and Pentair device. 

Interestingly it worked fine with a small 5-port switch connected between the two.  Eventually I found the Brocade switch port must be set to speed-duplex 10-full. 

After that the link became active.