This one isn't mine, but I saw it on LtU a while back. This isn't the exact error message (which I don't remember), but I believe it's from O'Caml:
O'Caml is strongly typed. The a' type can stand in for any type, as long as it's the same type everywhere a' appears. However, these types don't cross lexical scopes, so the above indicates two different a' types in two lexical scopes.
In my High School C++ class, one of my classmates found this jem out of VC++:
At which he replied "Oh, I'm ambigious?!!"
This one isn't out of a compiler, but caused me much grief. Last week, I was setting up a new Apache VirtualHost to run an SSL site. This would be the second SSL site we had (both within the same Apache config), but whenever I used the new domain, I kept getting the old site. After an hour of playing, I saw this line, right near the top of the Named-based Virtual Hosts docs:
Name-based virtual hosting cannot be used with SSL secure servers because of the nature of the SSL protocol.
At which point I went to find a hammer for use in bashing my skull in for improper RTM.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.