This article explains the step-by-step procedure to reseat the FPM module in the MX series router. 

These errors are seen when the chassis process (chassisd) is unable to read information from the I2C backup (I2CS) about the specified FPM board.

Mar  5 10:38:56.532 2025  root-RE0 chassisd[18459]: CHASSISD_I2CS_READBACK_ERROR: Readback error from I2C slave for FPM 0 ([0x2a, 0x21] -> 0x0)
Mar  5 10:39:57.212 2025  root-RE0 chassisd[18459]: CHASSISD_I2CS_READBACK_ERROR: Readback error from I2C slave for FPM 0 ([0x2a, 0x21] -> 0x0)

To clear the above error message a reseat of the FPM module would be required. Please take a safe MW to perform the below steps:

To remove the craft interface:

1. Discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis. 
2.  Detach any external devices connected to the craft interface.
3.  Loosen the captive screws at the left and right corners of the craft interface faceplate by using the Torx (T10) screwdriver.
4. Grasp the craft interface faceplate and carefully tilt it toward you until it is horizontal.
5.  Disconnect the ribbon cable from the back of the faceplate by gently pressing on both sides of the latch with your thumb and Remove the craft interface from the chassis.

To install the craft interface:

1. Discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis.
2. Grasp the cr-ft interface with one hand, and hold the bo‚om edge of the cr-ft interface with the other hand to support its weight.
3.  Orient the ribbon cable so that it plugs into the connector socket. The connector is keyed and can be inserted only one way.
4. Align the bottom of the craft interface with the sheet metal above the card cage, and press it into place.
5.  Tighten the screws on the left and right corners of the craft interface faceplate by using the Torx (T10) screwdriver.
6.  Any external devices connected to the craft interface.

Software Resync:

• After a reseat, a software resync of the FPM may be necessary. The following command can be used for that.
  
   labroot@re0> request chassis fpm resync