Off the top of my head I can think of Goldsmith's experiences with Ridley Scott while working on Legend. Goldsmith said it was one of the worst of his career, not only because Scott caved into the studio and let his score get dumped but because the process of working with him was so unbearable.

I've also heard that James Cameron made James Horner jump through numerous hoops when they worked together on Aliens.

John Barry had some harsh things to say about his experience on Born Free. I can't remember what exactly except he cited creative differences.

One of my favorites is the one of Jerry Goldsmith recording and mixing Start Trek:The Motion Picture just days before it's national release.

For years Goldsmith classified ALIEN as his most miserable working experience -- he was relatively happy on LEGEND until the score got tossed, because he'd gotten Ridley Scott to communicate. Failure to communicate with the director, in Goldsmith's view, is as bad as it can possibly get on any job -- hence these days, he seems to call GLADIATOR his worst experience, because director Rowdy Herrington apparently could not vocalize what he needed. I'm not sure where he's ever commented on another rejected score, THE PUBLIC EYE (he was probably the choice of producer Frank Marshall, who tries to get him on most projects, some of which -- SMOKE AND MIRRORS for example -- don't get made; and finally succeeded getting him for CONGO, ironically one of the very worst movies Marshall's been attached to. I wish Goldsmith had been secured for Marshall's production of THE SIXTH SENSE as well.)

NP: I'll reach into the stacks and grab something at random. Maybe I'll tell you what it is, and maybe I won't.

"No, I don't forgive him," Goldsmith said of Ridley Scott. "Why should I forgive him?" Once Scott read that, after having implicitly asked for Goldsmith's forgiveness through the reporter, that was probably the end of any chance they would ever get together again. He said at the time that he did hope he could work with Goldsmith again. Heh, that ends that. I am not sure, in the final analysis, that the two were ever very good for each other, anyway.

"Actually, I felt awful about having to replace Jerry Goldsmith's music on the American version, because Jerry had given me exactly what I'd asked for. And I still think Jerry's score for LEGEND was bloody good. But somehow, during all the second-guessing that went on while we were re-editing the film, Jerry's music began to be perceived as being too sweet; frankly, [Universal] got a little paranoid and thought Jery's stuff too sentimental. I was persuaded to be insecure about Goldsmith's score as well. . . . So it's all very, very sad. Goldsmith was upset by the situation, and we've never spoken since. After what he went through on ALIEN and then LEGEND, I doubt Jerry would want to work with me again."

Scott says he was "very insecure" after the commercial failure of BLADE RUNNER, and "that put me into the position of starting to believe what I didn't believe. So another way of explaining what happened on LEGEND was that I was being Hollywood-ized by the reaction to BLADE RUNNER."

Other horror stories includes Mark Isham and the Waterworld fiasco in which his score was replaced with a new one by James Newton Howard after Kevin Costner took over the directing chores after firing director Kevin Reynolds. Along with Alan Silvestri's miserable time on Mission Impossible after Tom Cruise fired him because his score was not what he wanted for the film. Of course there's George Fenton's rejected score to Interview With A Vampire in which the film's producers thought it was way too slow (Ironically it was reused and orchestrated for Mary Reilly), Thomas Newman's miserable experiences on The Craft and Pret-A-Porter. The infamous 13th Warrior in which Michael Crichton took over the project after the film was deemed unreleaseable firing John McTiernan (who still got credit) and completely throwing out Graeme Revell's score in favor of Jerry Goldsmith's brilliant work. James Horner's problems with Walter Hill on Streets of Fire in which he wrote 3 different scores and still had them thrown out in favor of Ry Cooder in which Hill would work with endlessly up until Supernova. Of course he then rejected Elmer Bernstein's score to Last Man Standing after the New Line music department was completely happy with his score and Hill just simply wanted Cooder on the project and thust was thrown out. Howard Shore's rejection of the Ron Howard thriller Ransom, in favor of a more conventional suspense score by James Horner. and the stories go on and on lol. but let's pay our respect to the scores of rejected scores past:

2 Days In The Valley (Jerry Goldsmith)
Marvin's Room (Thomas Newman)
Waterworld (Mark Isham)
Playing By Heart (John Barry 50% of it)
Prince of Tides (John Barry)
Mission Impossible (Alan Silvestri)
Assassins (Michael Kamen)
High Fidelity (Carter Burwell)
Gladiator (Jerry Goldsmith)
Die Hard With A Vengeance (Michael Kamen, the new material)
Alien Nation (Jerry Goldsmith)
Dead Bang (Gary Chang)
Rosewood (Wynton Marsalis)
Ransom (Howard Shore)
Dangerous Beauty (Rachel Portman)
Air Force One (Randy Newman)
Fair Game (Michael Kamen and David Sanborn)
The Bodyguard (John Barry)
Breakdown (Basil Poledouris, the first original score)
The Craft (Thomas Newman)
K2 (Hans Zimmer)
The Picture Bride (Cliff Eidelman)
Last Man Standing (Elmer Bernstein)
What Dreams May Come (Ennio Morricone)
I Love Trouble (Elmer Bernstein)
The Scarlett Letter (Ennio Morricone and Elmer Bernstein, seperate scores)
Streets of Fire (James Horner)
The Journey of Natty Gann (Elmer Bernstein)
A Low Down Dirty Shame (Bill Conti)
Young Guns (James Horner)
Legend (Jerry Goldsmith)
2001 (Alex North)
The Battle of Brittan (Sir William Walton)
The Horse Whisperer (John Barry)
The Sixth Man (Randy Edelman)
The Exorcist (Lalo Schifrin)
Halloween H20 (John Ottman)
Goodbye Lover (John Barry)
Interview With A Vampire (George Fenton)
Stepmom (Patrick Doyle)
The 13th Warrior (Graeme Revell)
Cruel Intentions (John Ottman)
Jersey Girl (Christopher Young)

I think the worst "film score war story" happened with revered British composer Howard Blake on FLASH GORDON. Rock group Queen was set to do the score, but couldn't really figure it out, so they hired Blake to do the almost two hours of underscore IN LESS THAN 10 DAYS!! Blake sat up the last four days and nights and wrote the entire score, delivered it to the producers and then slept for 3 CONSECUTIVE DAYS. His sleep was actually so deep that he needed medical assistance to wake up at all. He almost died!