hi TriKnight,

I know this behaviour from problems with EMC. Check also your power supply. Some cheap power-supplies don´t deliver a propper direct voltage and can cause such EMC-problems.

Also a FW-update can help. Try to update the FW to its newest version. you can find it here:

Firmware update for CPU 1211C, DC/DC/Relay, 6DI/4DO/2AI

 hope this helps,

regards,

I had a similar problem.  Performing a factory reset to the PLC let me download the project to the PLC again.

This failure may be more likely to happen if a project uses most of the available memory of the PLC. 

Updating the firmware may help.  Making sure the earth / ground / PE terminal on the power supply and PLC are both connected to the same point, and that the 0V terminal on the 24VDC power supply is also connected to that same earth / ground / PE connection is important - in case it is related to common mode voltage errors.

TriKnight

Thank you mopS04, I have tried replacing the power supply, but it was not worked. So the next step is to update the firmware.