Originally Posted by: Autohex_II_BMW 

we found the issue , to decrypt eeprom with key there is bug when you read file from CAS and click on edit direct you get that error, instead of that you just need to save the file and load the eeprom file then do the decryption it will work.
we will try to correct it on coming update.

That is Strange , I just had CAS 3+ and I was able to read Everything , But I had ECU with me , So first I enter Sk form ECU and Decrypt it OK.
After That I use working key just to test it and see is it same Sk and did fine. Only thing I did load again Eeprom when I did it with Key , But with ECU Sk I did it after I read CAS3+.

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yes sir that is no any error , if cas3+ you can read ISN only if you downgrade CAS. Also for other functions like key programming, key data saving etc. you need to downgrade.
yes sir this is what we are saying also, to decrypt with key you will get error if you did not load eeprom. straight way after reading eeprom to decrypt with key you get error. If you load eeprom and decrypt then no issue it will work.
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So, one more thing about this.

When, you get the "Cannot Read Key Pages" error, save eeprom file. Then close HexProg program, disconnect / reconnect HexProg hardware. Start the program and load the previously saved file.

Now it will read key pages and will decrypt.