Can't send messages to any users

Well I have 2 problems:

1st problem is:

Administer >> Autoresponder >> Autoresponder (send message) >> Then when I send a message, then enter "0" as the day of the message I get this error:
"warning: checkdate() expects parameter 1 to be long, string given in /home2/biblica/public_html/biblicalmission/includes/form.inc on line 1218."

2nd problem is:

I can't send any messages to any of the subscribers! I can only send a mass e-mail to only the admins.

I created a set called "Welcome" then I would register to that set and try to send myself a message to test it, nothing happens.

do I have to KEEP croning after every message? Also after the user subscribes is there away to make them get an e-mail that says "You are subscribed" and things like that?

ahh I've been at this problem for 2 weeks now, please help me.

Thanks