When a game is corruptible, its rules are too easy to break. This is almost always caused by a lack of clarity.
Corruptibility is not the same thing as brokenness. Corruptibility refers to how difficult it is to follow all of a game's rules correctly. Brokenness refers to the inability of a game to function properly, even when you do follow all of its rules correctly.
A game may become corrupted because you don't notice that you've done something illegal, like moving a piece further than it's allowed to move, or placing a tile in an illegal location.
A game may also become corrupted because you forget to do something that you're supposed to do, like advancing a marker when some particular event occurs.
A game will be prone to corruption if it contains memory-conditions—aspects of the game-state that are not explicitly tracked by any of the components, but must be remembered in order to follow the rules correctly.
As a designer, you cannot completely eliminate the possibility of corruption from your game, but you can reduce it, by increasing the game's clarity. If a particular type of corruption occurs over and over again in your game, that indicates a problem with the rule-set or the components, not with the players.