On Windows, when having an error with a unicode symbol lurking around, GHC fails to print its name. So e.g. you get a message of an error "In the first argument of (<stderr>: commitBuffer: invalid argument (invalid character)".

I am not certain, but I think that the fix would be to hSetEncoding stderr utf8 before the output is printed. If so, hopefully it should be a quick easy fix. (And perhaps it would be appropriate to do the same for stdout as-well).