Fail to add assertion

My environment is Ready API 1.7.0

I imported an existing project created by others.

And I tried to add an assertion to a new test case i created.

I click the green "+" icon and select a REST request as source.

The property shows "response" and I double click assertion [Contains] to add it but fails.

The column of my assertion remains empty.

However, i can add an assertion to the existing test case.

Is there any setting about test case and REST request that i miss ???

Thank you.