Sending Mails through Application Engine (SMTP Configuration).

Hey, I have developed an app engine which will have to send emails to users for certain condition. I'm using PT_MCF_MAIL Package and PT_MCF_MAIL:MCFOutboundEmail but it going in %ObEmail_FailedBeforeSending. But when I use same code on some button and then trigger the button from the page. it works fine and mail is delivering fine. I wanna know what thing I'm doing wrong. Below is the mail code.

import PT_MCF_MAIL:*;
Local PT_MCF_MAIL:MCFOutboundEmail &eMailUserProfile = create PT_MCF_MAIL:MCFOutboundEmail();
&eMailUserProfile.Sender = "someone@example.com";
&eMailUserProfile.ContentType = "Content-type: text/html; charset=utf8";