Hello. There is a problem with Siemens S7 300. We got a replacement PLC but it does not run the program from the MMC. The new PLC is dated 2011 while the old one is 2018. Both have the same firmware v. 3.3.12. The only difference seem to be their hardware versions. The old PLC has hardware v. 5 and the new one has hardware v.4 We managed to restore the old PLC and it's working fine now.