Dear Dzaky
as i guessed you've entered too many known parameters for your sources and sink. you must set one of the "P and Q" for a source or sink. I suggest set Q for the wells and P for the sink. Double click on the wells and delete P value and then remove Q value from the Sink. If you do these right, you'll see below the wells Q (current: PQ) and below the Sink P (current: PQ).
Keep on Engineer!