When Sheldon proclaims that he has an ulcer, his mother reminds him that he also thought he had "mad cow" disease in the past. The first case of bovine spongiform encephalopathy being transmitted to humans as new Variant Creutzfeldt-Jakob disease was identified in 1996, 7 years after the show's timeline.
While Sheldon is at the doctors office, he attempts to log into NASA using a modem. The modem should have been V.32, developed in 1984 but not sold until 1988 at a cost of ~$2000. The sound the modem makes upon connecting is actually V.34, developed in 1994, which is five years after the episode's time period.
The logo on the NASA patch Sheldon is given wasn't in use at the time of the show. It was active 1959-1975 and then again from 1992 to present.