I tried to run cooling over the eroupters and it seemed to interfere with them (maybe magnetically?) ,so I just leave them as is. I'll have to hope the boards run at a decent temp though I've got a fan ready to try and place when they get here.
Was the fan you were using a USB fan plugged into the same hub (Assuming BES, not BEB) or otherwise on the same 'power circuit' internally? Could have been the power draw affecting the BE's ability to function under load (unless the fan was introducing electrical noise into the power lines for the BE's?)
I reached the same conclusion with BE's, so for all of my USB miners the fans are powered from a separate hub which is usually not connected to the PC running the hashing control software.
Now running a mix of BE's, BF, RF (Red Fury) and Drillbit Thumb all on the same old laptop. The bitfury chip based miners happily share the same hub, some running on bfgminer and the Thumb on cgminer.
Cheers