Dear Durrani,
Did you connect a networking between PLCs by using RS485? If yes, how many PLCs did you connect? Can you tell me more about the condition when you got the problem?
I also face to the problem that you mentions before. Electrical noise is modifying either the RAM content or the EEPROM content or both and is therefore giving you all kinds of problems you mentioned.
Is that only this 4 error occurs? If yes, may be the the EEPROM chip M2017P not yet fully damaged and may be we still can rescue it, I hope not too late.
1) If you have using RS485 network, try to remove the 75176 or 75HVD3082 RS485 driver IC. (May be the damaged IC is 75176 or 75HVD3082 RS485 driver IC and not the EEPROM chip M2017P)
2) Please off power for that PLC to rest not less than one day.
3) You can use Dos version TriLogi program to remove the password. (This will clear the program in PLC also, so, you need to re-transfer the program to the PLC.)
4) If you have more than one PLC, then you can exchange the EEPROM chip M2017P and try to detect the condition of both PLC. (Which PLC still have problem?)
5) Try to use another power supply.
6) If you have using RS485 network, temporary remove the RS485 network cable.
Thank you