ML320, O2 Sensor Replacement, Engine Code

Hi,

 

I have a Mercedes ML 320, 2000.

 

I just replaced all four oxygen sensors but the "Check Engine" has returned right after the replacement. 

 

The codes that have been indicated: 157, 161, 135, 155, 141 and 134.

 

Do you know why those codes would appear even with all brand new Bosch oxygen sensors? 

 

I am so puzzled...

 

Thanks,

 

Emily