Here is a dump of the error:

kingix is NIL!!!  color=-1... about to crash
./nchess6.rb:1924:in `[]': no implicit conversion from nil to integer (TypeError)
        from ./nchess6.rb:1924:in `Eval'
        from ./nchess6.rb:1918:in `each'
        from ./nchess6.rb:1918:in `Eval'
        from ./nchess6.rb:1781:in `Eval'
        from ./nchess6.rb:2407:in `ABnegaSearchZWTail'
        from ./nchess6.rb:2383:in `times'
        from ./nchess6.rb:2383:in `ABnegaSearchZWTail'
        from ./nchess6.rb:2457:in `ABnegaSearchZWTail'
         ... 11 levels...
        from board.rb:1028:in `PrepareForNextMoveWhenOpponentThinks'
        from board.rb:812:in `replaystart'
        from board.rb:230:in `build'
        from board.rb:1079 

Note that this could be worked around, but shouldn't be...
This indicates that there are fundamental bug(s) in the chess engine
that need to be fixed.

The biggest challenge with this port was that zero (0) evaluates to TRUE
in Ruby but evaluates to FALSE in Python (and Perl), unfortunately.
I believe it is this kind of logical checking somewhere that is causing this problem.

I've provided the original Python source so that line-by-line comparisons can be made (even though the line numbers
don't match up exactly, you know what I mean).

-- Glenn