In Mirc a DCC send error for local host normally means that your mirc has not gotten the proper External IP address to use.
Look in Options, Local Host and see what it has for your IP address.
If it has a 192.x.x.x it is not correct.
On your linksys router, go to the status page.
There you will find your external IP address.
Just type that IP address into the local host settings dialog box for the IP address.
Your post says you have followed the instructions for having the linksys router do the port forwarding properly, so this will be the problem.
I know cause it did happen to me. I do use a Linksys router and i followed the instructions for the forwarding of the ports for mirc to use for dcc and was not able to send.
SPR Jukebox only sends to people when they use the proper request command.
You will not be able to send with SPR unless you can manually use the /dcc send command to send a file to someone else.
whenever you have a problem sending a file, try using the normal mirc /dcc send <nick> <file1> command.
This will tell you that mirc is having the problem and not the script your using.