As per my understanding, you have chosen fixed-step solver to run the test harness with a step size of 0.5 and then chosen a sample time of 0.2 for your test sequence block. This results in an error as a fixed step size of 0.5 will not be able to cover the rate of execution of test sequence block since 0.2 is less than 0.5. The sample time of all blocks in the model has to be a multiple of solver step size. Alternately, you can also choose a variable-step solver to execute your test harness, by which the solver will automatically choose time steps to cover step size requirements of all blocks included.
Sample time of test sequence block can be modified by opening configuration parameters in the test sequence editor.
Refer this link to read more about sample time and its different types.