Hi Chiara,
for this kind of questions (when one gets an error message) it's always more efficient that one contacts our [b]Tech Support[/b] (mikebydhi@dhigroup.com) because the situation may be very specific and more importantly because one may need to send some attachment.
In your case, I would like to see the full content of the log (Logging Pane). So the best is that you: 1) clear the logging from the Getting Started; 2) start your project; and 3) do whatever action (launch the simulation?) that results in that error. Then [b]send the Loggin Pane[/b] (in xls format).
More in general regarding setting up an SBR model, indeed it may not be that straight-forward, primarily because it's got phases (fill, reaction, ..) and it therefore needs to be fed (i.e. receive inflow) at the right time. Which requires some level of control (timer, controller, buffer tank, ..).
A [b]new SBR Tutorial[/b] is going to be added to the new release: so, once more, if you contact the Tech Support, you might even get it to get inspiration.
Not sure if you have already done this, but there are a [b]couple of threads[/b] on this Forum dealing with [b]SBR modelling[/b]: you may want to check them out.
