cAP With rb951

hi all
strange one this .
I was told to use port 5 to attach to cAP from mikrotik rb951 , but when i do this the cAP is not discoverable in capsman but when i use a POE Injector from port 4 it picks up no problem.
I have tried various routers so its not just 1 specific device .
Any ideas?


thanx for your time

mke