Navx Trouble - inconsistent connection

[techplex]

a.)

I can confirm that we tested the NavX connected via USB and via the MXP port and the only code change between the two was

serial_port = new SerialPort(57600,SerialPort.Port.kUSB);
-- to:
serial_port = new SerialPort(57600,SerialPort.Port.kMXP);

b.) We tried the Navx with the NavX UI and did not seem to have the same disconnect issues.
We then reconnected the NavX to the RoboRio and continued to have the same disconnect issues.

I'm beginning to think its a bad board. I tried changing the update rate from 50 to 60 to 30 and saw no difference in the disconnects.

Thoughts?