Hey all..
Very perplexing problem. Got an RB153 w/48v PS that dies when connected to my netgear switch via poe, however I can unplug from the switch and plug into my laptop and everything works fine. So I get a different switch, plug it in and the RB 153 dies, plug my laptop into the switch, communication normal. The RB153 simply refuses to operate plugged into a switch, which is absurd because its been running like that for months. Got to put in a rush order to get a replacement, meanwhile does anyone have a clue as to why, all of a sudden, this board refuses to operate connected to a switch but works fine connected to a laptop? 
Is the 153 rated to 48v? I’ve never used one so I don’t know, but can you try a different power supply? Maybe 24v.
You might want to try turning auto negotiation off in the ethernet interface on 153. I’ve seen some weird problems with auto negotiation and auto mdix(auto crossover) failing on some switches/devices.
48 volt is fine for the RB153’s so that shouldn’t be a problem..
-Gerard
Update…
Grabbed a voltmeter and made some measurements on the cat5 data output of the poe injector. For some unknown reason the RX lines (pins 1&2 of the cat5) now have 48V dc. The power/data ports of the injector only supply power to pins 4&5(+) and 7&8(-), and that is only on the other side of the injector (power/data). So, somehow the mikrotik board has bridged/shorted the poe supply voltage onto pins 1&2 of the cat5. Evidently my laptop ethernet port is 803.3af compliant (thank goodness) as it survived and didn’t kill the ps permitting the mikrotik to power up and function ok. So i guess my quick fix is to custom make a split cat5 cable with one termination loaded on pins 4,5 & 7,8 for the poe supply and another for 1,2 & 3,6 fed to ether2 for data comm to the mikrotik. Hopefully this will do for the time being.
update 2…
that worked…up and running 