The error code "2100" is "SP.UNIT LAY ERR.". This error may be caused by one of the following factors.

(1) An intelligent function module is assigned as an I/O module, or vice versa.
(2) In the I/O assignment setting of the PLC parameter, switch setting is made for a module that has no switch setting.
(3) In the I/O assignment setting of the PLC parameter, the number of points assigned to the intelligent function module is less
     than the number of points of the connected module.

Refer to the following remedies.
(1) In the I/O assignment setting of the PLC parameter, set the I/O assignment again so that the setting matches with the mounted
     status of the intelligent function module or the CPU module.
(2) In the I/O assignment setting of the PLC parameter, delete the switch setting.