Redundancy error OB72

Hello Gents,

We have redundant system on  HVAC AHU system ,  one of the  PLC 412-5H PN/DP (FW v6.0.4; boot loader 6.00) has failed,   replaced with new  CPU with the same order 6ES7412-5HK06-0AB0 but FW 6.010 and boot loader 6.0.1. 

Uploaded backup project to the new PLC - doesn't go to RUN - came up with Error OB72 - system program different. 

Due to operation reasons could not stop HVAC so that Downgraded new PLC to FW v6.0.4. boot loader remains 6.0.1.

Now we have  Redundancy error OB72 - Link Up - update aborted  due to configuration change 

Gents, Could you please advise 

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Split from Problem with redundancy system.

Closed cause question posted twice.

The second thread with the subject Event ID 16# 73C1 is published within the conference SIMATIC S7-400 / S7-400H / S7-400F /FH.