A screengrabber is used to grab images from a source like the Sci-Fi Channel's live broadcast or a database of stored images. The screengrabber will then move the image to the caption area for the cappers to enjoy. Sometimes, this goes wrong. When the screengrabber stops working, the caption area will either show no image (see The Red X), or stick on the same image indefinitely. Scifi.com's Caption This! was famous for the latter, freezing on one grab for what would sometimes be days at a time. Complaints to the webmasters tended to reveal how low a priority C.T! was to the site, especially after MST3K's cancellation.
Cappers being cappers, we would often go to Kevin Sorboid lengths to come up with captions, again and again, for the same image -- leading to a remarkable example of something, I don't know what. Probably nothing good. Phil and Bob One of the most famous frozen screengrabs occurred during a 1999 Caption This! screening of Psycho II, when the site froze on a grab of Anthony Perkins and Robert Loggia for 37 years. cScott curated a gallery of the captions from this nightmarish event here:
And years later, when Jazzsoda added "Psycho II" to the HCC catalog, he duplicated this same screengrab 20 times in a row in homage to the bad old days: