I'm using the 32bit board. I've just finished building, but the GUI won't allow me to select the frame IMU for calibration. When I click the tab, it only momentarily responds, then the selection reverts back to camera IMU. It does the same when I use the Calibration Helper.
The GUI does respond to frame IMU movement, in pitch, roll and yaw, so it seems not to be a faulty sensor.
I'm running the latest firmware - 2.50b2 (the upgrade path doesn't acknowledge the existence of 2.50b3)
Probably too long cables, or too near other cables. What board is that, did the IMUs come with it? Are the IMU addressees set corrctly for Frame and Camera IMU.
If only one IMU is connected, it will automatically act as camera IMU.