Don't you know that Douglas Adams references are off-limits to true HHGG fans until people forget about the movie? Anyone mentioning "42" is bound to look as if they only heard about it now.
Any of the TCP errors (63, 56 and so on) can be enough to drive you mad if you can't see any good reason for it being generated.
The PDA module has seperate error codes for the same errors (in the 10000 range), which can also be annoying.
There is, of course, the all time favorite - ERROR 1 - Invalid input.
But, after all of those, there is only one error code I really like - 0. That's like sweet music to my eyes.
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Try to take over the world!