Deadlock from Crate / Oil Drum floating on water
From Worms Knowledge Base
If a game uses a map with indestructable borders on all four sides and the water level is higher than the height of the bottom border, this glitch can be inadvertently triggered.
When a crate of any kind falls into the water, it will get stuck in the water where the bottom border would be. This could be triggered by anything that causes a crate to fall into the water - including Earthquake, Nuclear Test, or even a simple water rise in Sudden Death.
This results in the game eternally waiting for the crate to sink, and players would have to quit the game. If the glitch occurs during a round winning event, there would be no way to exit the game.