webbrickmon is getting reports from 10.100.100.100.  Can't get a 'browser'-type connection though.

 Using webbrickmon to reset the brick's address doesn't seem to stick; on next report packet, address is back to 10.100.100.100.

now clueless......
 

I am assuming single webbrick on the network.

Possible problem is that some low end network switches do not handle correctly fallback to baseline ethernet (10Mb half duplex) and end up configuring the port as 10Mb full duplex. This causes communication problems with a webbrick. The UDP packets received by webbrickmon are broadcast, and small payload (less than 20 bytes) and are not affected by this problem.

So suggest try changing the hub/switch.