What causes the 'fatal error' in Sonic games, particularly older titles?

The 'fatal error' in classic Sonic games (like Sonic 1, 2, and 3 & Knuckles) is typically caused by attempting to perform actions the game wasn't designed for, often involving specific glitches or exploits. These can include exceeding the maximum number of rings allowed (usually 99), triggering out-of-bounds areas, or manipulating the game's memory in unintended ways. The error is a built-in safeguard to prevent crashes or data corruption.