What do CBS’ Picket Fences and Fox’s The X-Files have in common? Not David Duchovny, star of the latter, despite the best efforts of both shows’ producers. It all began one night when X-Files’ Chris Carter and Fences’ David Kelley were on their way to the parking lot at Twentieth Century Fox, where both shows are produced. After talking about their shows’ shared viewership (Fences follows X-Files’ time slot on Friday nights and both have a large 18-to-49-year-old audience), they hatched a plot that would begin on X-Files and wrap up on Fences. ”I wrote a script and showed it to David (Kelley). And he liked it and decided to continue the story,” says Carter. The X-Files episode is set in a small Wisconsin town where the locals suspect that their cows are being injected with alien DNA. The story was supposed to continue when Duchovny’s character showed up in Fences’ Rome, Wis., where similar problems were occurring. CBS, however, apparently nixed the idea and Duchovny’s role was written out. A Fox source insists, ”what CBS can’t and won’t dispute is that they were unwilling to help another show on another network.” Says Michael Pressman, Fences’ coexecutive producer: ”As much as we understand CBS’ position, we are disappointed not to have David in Rome.” Officially, Fox television is denying that a crossover episode exists, which comes as a surprise to Carter and Pressman, who say the X-Files episode will air on Dec. 9, with a Fences follow-up (without Duchovny) the next week.