"I was in New York. Hitchcock was in California. He rang me to make a report on his progress and said, I'm having trouble. I've just sacked my second screenwriter"

This quote is most likely referring to the making of a film. Hitchcock, the director, remains in California and Patricia Highsmith is in New York. Hitchcock is calling Highsmith to report on his development and he is having problem. He has just fired his 2nd film writer, which suggests difficulty. This might mean that the script is not going as planned or that the film writer was not satisfying Hitchcock's expectations. It might likewise suggest that Hitchcock is having problem finding the ideal individual to compose the script. Whatever the case, it is clear that Hitchcock is having trouble with the task and is looking for assistance from Highsmith.