Signal loss after a short time

When running both usrp_oscope and usrp_fft, I lose the signal and the
GUI becomes unresponsive after 5 - 30 minutes of operation. I had
previously ran this system for more than 24 hours with an installation
on a laptop back in July. Here is a short summary of my setup:

  1. Dual HT Intel 64-bit processors with 32-bit Gentoo distribution.
  2. Latest dependencies from the portage tree (using ~x86 flag).
  3. I am using an external clock at 64MHz that will sync the USRP with
    the rest of my system.
  4. I have an official USB 2.0 certified cable.

To get the system back up and running properly, I either cycle power
(unplug the power supply) or run the usrper load_standard_bits command.
I also receiver failures when running the benchmark_usb program maybe
this is beginning to sound like a hardware problem ?

–Ryan