To expand on that, you need to do 2 things.
First, reprogram the obi, and make it FORCE connect 100meg/full duplex. For some reason, the obis are only conencting to network devices at 10meg half duplex. This should fix a majority of problems.
Force OBi to 100Mbit/Full duplex.
Press *** 0 option 27#, press 1, value=1#, press 1 to save, then hang up phone
If that don't work, then put it on its own subnet.
All your normal lan on 255.255.255.0, then create a VLAN with 255.255.255.128