Two ways:
First, create a variable, let's call it <Non Zero Response>
:
=If <Response Code> <> "00" Then <Response Code>
Then in the report block:
=Count(<Non Zero Response>)
The second method works, but I'm not sure why. So I can't be sure it will work in all versions:
=Count(=If <Response Code> <> "00" Then <Response Code>)