Have you encountered the issue again since implementing the fix??? I have the same issue and the fix above did NOT solve the problem for me. It still hangs on:
setClockSource(MPU6050_CLOCK_PLL_XGYRO);
I've been using the MPU-6050 (on the GY-521 board) over the past year with an arduino (several different versions) and now a teensy 3.1 and I still get the same error. I've used used several MPU-6050 boards and each produces the same error, but randomly/intermittently like you are/were experiencing.
When I do encounter the problem, cycling the power on the MPU-6050 doesn't seem to fix the issue..it still hangs on "setClockSource." Reseting the main MCU doesn't seem to fix it either and I get the same error. I have to fully cycle the power on both the main MCU and the MPU-6050 to get it working again.
Have you had any other success or fails with this issue?