[Plugin: Sendit Newsletter] How users subscribe

Hi, I have created a subscription form. Its code is:

<!– Start Sendit Subscription form –>
<div class=”aside-col-1 border-right-2″>
<h3><span class=”clr-1″>N</span>ewsletter:</h3>
<form id=”form-search” name=”theform”>
<!– the shortcode to generate subscription fields –>
{sendit_morefields}
<span>Enter you email here:</span>
<input id=”email_add” type=”text” id=”sendit_subscribe_button” name=”email_add”/>
<input type=”hidden” name=”lista” id=”lista” value=”{list_id}”><div id=”sendit_wait” style=”display:none;”></div>
<input class=”button” type=”button” id=”sendit_subscribe_button” name=”agg_email” value=”{subscribe_text}”/>

</form>
</div>

The CSS of the form is:

.aside-col-1 {float:left; width:173px; padding:0 34px 0 37px;}
#form-search {margin:12px 0 0 0px; overflow:hidden; width:173px;}
#form-search span {display:block; margin-bottom:5px;}
#form-search input { width:151px; height:15px; font-family:Tahoma, Geneva, sans-serif; font-size:12px; color:#4d4d4d; border:#c0cdd3 1px solid; background:#d9e1e4; vertical-align:top; padding:4px 10px 6px 10px; display: inline-block; float:left; }

/*DO NOT CHANGE THIS ID*/
#sendit_subscribe_button{margin:5px 0;background:#ff9900;color:#fff;}

.short{
width: 100px;
margin-bottom: 5px;
}

#submitbutton{

margin-top: 5px;
width: 40px;

}

.info, .success, .warning, .sendit_error, .validation {
border: 1px solid;
margin: 5px 0px;
padding:10px;

}
.info, .notice{
color: #FFD324;
background-color: #FFF6BF;
}
.success {
color: #4F8A10;
background-color: #DFF2BF;
}
.warning {
color: #9F6000;
background-color: #FEEFB3;
}
.sendit_error {
color: #D8000C;
background-color: #FFBABA;
}
.aside-col-1 small{font-size:0%;}

The problem I am facing is that when user writes an email address in the text field and click Subscribe button, no subscriber is added in the mailing list.
Plz someone tell me the solution as soon as possible.

http://wordpress.org/extend/plugins/sendit/