so i got the pda apps sprint sms on my t600 and it was working fine, actually really well

today i tried smsing someone and it said it could not send it, error 19

the only person i can send messages to is someone i had a previous convo thread with in my message inbox, if i try to send a message to anyone else i get error 19

your thoughts please?

what should I do about this?

has this happened to anyone else?