Hello John,
The E310 is designed to have GNU Radio run onboard the radio rather than on an external computer. By default the USRP driver does not include support for using the E310 remotely across a network. This is because network mode was implemented primarily as a debugging aid. The sample rate which it is possible to stream across the network is very low.
If you do want to stream samples across the network you will need to compile UHD with custom settings. Also please note that the version of UHD on the host computer must exactly match the version on the E310. You can find out this version by connecting to the E310 using SSH or the USB serial console and running a uhd command, which will print the UHD version.
http://files.ettus.com/manual/page_usrp_e3x0.html#e3x0_network_mode