If I recall correctly, this was over Eddie Murphy's "Coming To America." Art Buchwald wrote and pitched a script that was passed on, yet later produced almost identically.
J. Michael Straczynski claims the same thing happened to him when he pitched Babylon 5 to Paramount, who passed. Then not too long after that Star Trek: Deep Space 9 debuted, and there were some noticeable similarities between the shows.
As a big fan of B5 and a minor fan of DS9, I always found the "whole series was a copy" claim ridiculous. The similarities between the shows were often tangential. A lot of the things that were actually similar, like the fact that both series focused on large space battles, were most likely because of technology (ie, the ability to render large space battles) rather than the DS9 writers stealing from the B5 script. The shows as a whole follow wildly different trajectories.
The only version of the theory I've heard that made any sense is that studio execs who knew of both shows (which were being developed simultaneously, not particularly inspired by each other) may have taken ideas they liked from B5 and suggested them in a very conceptual way to the DS9 writers ("how about having a ship in addition to the station, so we can have some occasional planetary adventures?")
