I have been going over this conversation that was started by thehypnominer.  I have a situation that precisely mirrors this person's issue, but after going through this thread I don't see that his issue was resolved.  I have an ongoing problem that my miners go into a ZOMBIE mode, and sometimes an OFF mode.  But most of the time it is ZOMBIE.

It happens anywhere from 1 hour to 12 hours after I plug them in.  I have tried different computers and different USB hubs.  I have not increased the voltage and don't even know how at this time.  They are running at 100 MHz.  And I have even decreased the freq parameter down to 100 in cgminer.  Whether I plug in both USB miners at the same time, or separately, this happens. 

The only thing that I can think of is that there must be some recommended USB hubs that I should be using.  I have read that some USB hubs don't give the amount of power that they seem to tout on their packaging.  If that is the case, can you please suggest a particular USB hub that I should purchase?  If this is not the solution, could you please let me know what to do?   Like thehypnominer, I had been planning to buy 10 or more of these things, but the first 2 that I purchased seem to give me a never ending road block. 

I'd try increasing the voltage a little bit. How to do so is referenced in the first post.