Because the V2.4.06 version have a little specificity.
So please in the OLT CLI command upgrade to V2.4.06 version

Upgrade Topology:
 PC  IP address:192.168.x.x                 MGMT IP address: 192.168.y.y
  PC(tftp-server)---------------------------------OLT

Upgrde Step:
1.upgrade FD11XX_V2.4.06_210104_X000.img file and then reboot OLT.

2.upgrade FD11XX_V2.4.06_210104_X000.img file again but don't reboot OLT.

3.upgrade FD11XX_FW_V2.4.06_201111_1751_X000.img file and then reboot OLT.

Upgrade Command in the OLT CLI:
system update firmware FD11XX_V2.4.06_210104_X000.img  tftp-server 192.168.x.x
system update firmware FD11XX_FW_V2.4.06_201111_1751_X000.img tftp-server 192.168.x.x