On some servers a pipe is not possible, or the path is different, due to server configuration. The fastest way could be to ask your host how it's done on your server.
You may want to try adding "/usr/bin/perl" to the command-line, ie:
|/usr/bin/perl /home/xxxxx/public_html/cgi-bin/signup-list4.cgi
Also make sure there are no trailing spaces, etc.
Regards