bug in c# generator?

Hi, I'm writing a c# parser using antlr, and I've come across a
problem that I can't figure out, where a '$' character in a
single-line comment isn't being recognized as a valid character
(unexpected char: '$')
The rule is:

SL_COMMENT:
        "//" (INPUT_CHARACTER)*{ _ttype = Token.SKIP; } ;

protected
INPUT_CHARACTER:
        ~('\u000D' | '\u000A' | '\u2028' | '\u2029');

options:
 k=4, testLiterals=true

and compiled as: antlr.Tool mygrammar.g

I can't find any other characters that cause this problem, and trying
to trace through it leads me to
  tokenSet_1_.member(LA(1)) = false when LA(1) = '$'

tokenSet_1_ is large and indecipherable to me, but I can post it here
if anyone needs to see it.