ReadyAPI/functional test assertion don't works after awhile!

Hi 

I am using ReadyAPI 3.5.1

I have already defined some test suite and test cases to meet my requirements for test and controlling my API functionality , and it worked fine so i save it and in every new version of my production i try to use already save test cases. 

But funny thing happen! 

I have some simple Assertions in my test cases to control the error messages i expect.

For example i am going to control error message "KEY_UNRECOGNIZED"  , so i had defined an Assertion for response match content and it used to works! but when i try to run the test and control it again after a week , i see that these assertion do not correctly recognize the response error message ! (attached screen capture of it )

So as you can see i supposed to look for "KEY_UNRECOGNIZED" and  in response it has "KEY_UNRECOGNIZED"  and in my case it matched so it supposed to PASS , but i show FAIL ?! 

please note that this test step used to works fine while ago and i have done no change to it ...but it don't works correct now ?