the error message refers to $param being undefined...

it looks like the parameter name is not defined and (in my version of CGI.pm at least) this looks like a problem...

# from CGI.pm

sub parse_params {
    my($self,$tosplit) = @_;
    my(@pairs) = split(/[&;]/,$tosplit);
    my($param,$value);
    foreach (@pairs) {
    ($param,$value) = split('=',$_,2);
    $value = '' unless defined $value;
    $param = unescape($param);

# this is where the situation goes unchecked...
# CGI::Util::unescape returns undef if $param is undef
# none the wiser and no error checking!

    $value = unescape($value);
    $self->add_parameter($param);
    push (@{$self->{$param}},$value);
    }
}
[download]

so my guess is that you have a URL like:

http://your.site.here/cgi-bin/script.pl?param1=value1&=value2&param3=v
+alue3
[download]

which is lacking "param2" and would cause the issue you are seeing. try adding...

next unless defined $param;
[download]

where I put the 3 line comment inside the parse_params sub

hope this helps

update: if this does turn out to be the problem you may want to check if the most recent version has the same problem - if so you can email the author(s) and let him/her/them know you have discovered a bug

   larryk                                          
perl -le "s,,reverse killer,e,y,rifle,lycra,,print"