Generator X Response from Runner

Hello everyone, I'm having some problems with the loadui tests. I have to control the generator tests, I need to generate a new request only if only I got the response from last request. It's a very important feature.
I have used the "Fixed Load" set at LOAD = 1, and something the runner execute twice at same second, and this give me error.

It can be some kind of error at the test, or I need o use another generator?

THanks all.