strange Prelude.chr bug

[Malcolm Wallace]

I have a program (a compiler in fact) that, when compiled with hbc
or nhc98, gives the following (correct) output at runtime:

    Couldn't simplify the context ((_161) _160).
    Possible sources for the problem are:4:19

but when compiled with ghc-4.06, it gives the output/error message:

    Fail: Prelude.chr: bad argument

Now first, there is no Haskell'98 function Prelude.chr, and second,
my program does not use *any* function called chr.  So what might be
going on?

Regards,
    Malcolm