Complex sentence: Before production began Rivers assumed that it was a film script and that he would be paid for his efforts while Dean Learner assumed that one could make a television series without being asked by a TV channel; both were mistaken.
Split into simpler sentences: Before production began Rivers assumed that it was a film script and that he would be paid for his efforts. And Dean Learner assumed that one could make a television series without be asked by a TV channel; both were mistaken.