Brad Pitt’s “World War Z” was plagued with on-set drama, budget issues and a weak ending that had to be entirely reshot. Pitt, the star of the upcoming zombie apocalypse thriller, called in “Lost” co-creator Damon Lindelof to clean up the script. With a budget that ballooned to about $200 million, the film would need to rake in $400 million worldwide to break even, according to an upcoming Vanity Fair cover story. Pitt pushed the boundaries, demanding R-rated violence, while Paramount made it clear they wanted to keep it PG-13. Tensions peaked on the set when it was rumored that Pitt wasn’t speaking to director Marc Forster. “It was literally insane,” said Paramount President of Productions Marc Evans. And when it came time to watch the director’s cut, Vanity Fair reports, the room was silent. “It was, like, ‘Wow. The ending of our movie doesn’t work,’ ” said Evans. “I believed in that moment we needed to reshoot the movie . . . We were going to have long, significant discussions to fix this.”