Hello All

I got some problem on triggers .I am try to send a group mails by using triggers on custom object.

 I got this error message"INVALID_TYPE_FOR_OPERATION, Only Users, Contact or Lead allowed for targetObjectId ".

Can't we send group mails on coustom object by using a triggers.PLZ help me any one in this problem.

my code:

trigger RoomExpensesTrig on Rooom_mets__c (after insert) {

if(trigger.isInsert&&trigger.isAfter) {
Rooom_mets__c con1=[Select id from Rooom_mets__c limit 1];

List<Rooom_mets__c> emailID = [select Email_id__c from Rooom_mets__c];

String addresses;
if (emailID[0].Email_id__c!= null) {

addresses = emailID[0].Email_id__c;

for (Integer i = 1; i < emailID.size(); i++){

if (emailID[i].Email_id__c != null)
{
addresses += ':' + emailID[i].Email_id__c;
}
}
}

String[] toAddresses = addresses.split(':', 0);

EmailTemplate et=[Select id from EmailTemplate where name=:'VFTmpToEmail'];

Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();

mail.setToAddresses( toAddresses );
mail.setTargetObjectId(con1.Id);
mail.setSenderDisplayName('LAKSHMI3VENI');
mail.setTemplateId(et.id);

Messaging.sendEmail(new Messaging.SingleEmailMessage[] {mail}); 


}
}

how to achieve overloading in webservice in salesforce