What did you actually try (show your code)? What does that asp page expect? What is actually sent over the wire ( http://wireshark.org, Live HTTP Headers)?

#!/usr/bin/perl --

use CGI();
my $data = 'http://bar/?%2fb=c;d=e';
my $uri = 'http://foo/asp.asp?'.CGI::escape($data);
print CGI->redirect(
  -nph => 1,
  -uri => $uri,
);
__END__
$ perl test.pl |cat -v
HTTP/1.0 302 Found^M
Server: cmdline^M
Status: 302 Found^M
Date: Sun, 01 Mar 2009 06:57:57 GMT^M
Location: http://foo/asp.asp?http%3A%2F%2Fbar%2F%3F%252fb%3Dc%3Bd%3De^
+M
^M

# perl test.pl | cat -v
[download]

There's no need to actually LIE, no such thing as LWP::Post