ads differential port reference plane

Hi friends,
I want to set mom differential port in the same reference plane,but fail,and shows error as attached message.How can i set differential port in the same reference plane?
Thanks,

It is not error message but warning. This warning can be eliminated.
First set port 1 as differential need not give associate number , then select port 2 and set as differential port now you assign associate number.
If you see the 3D view now it will be OK.

Thanks,kspalla.Follow your suggestion,still be same.I use ADS2009.And attached my file,can you help me analyze it?
Thanks.

Note that mom_ref_offset line should touch both the ports.
The same can be observed in this updated file.

You are my lifesaver.Thanks for your help!