Java Script issue - referencing record type
I am following up after a consultant that used JavaScript to direct users to 1 of 2 record types from an Account Related List. I have added a 3rd record type, and am trying to create a button that references the JavaScript. Here is the code that I am working with:
{!REQUIRESCRIPT("/soap/ajax/31.0/connection.js")} 
{!REQUIRESCRIPT("/soap/ajax/31.0/apex.js")} 

var opportunity = new sforce.SObject('Opportunity'); 

opportunity.Name = 'Do Not Delete'; 
opportunity.AccountId = '{!Account.Id}'; 
opportunity.RecordTypeId = '{!$Setup.Opportunity_Record_Type_Ids__c.Record_Type_3__c}';
opportunity.StageName = 'Quote in Progress'; 


var closeDate = new Date('{!TODAY()}'); 
closeDate.setMonth(closeDate.getMonth()+6); 
opportunity.CloseDate = closeDate; 

var result = sforce.connection.create([opportunity]); 

if(result[0].success == 'true'){ 
var serverPrefix = '{!$Setup.Server_Prefix__c.Server_Prefix__c}'; 
var oppId = result[0].id; 
parent.window.location.href = 'https://' + serverPrefix + '.salesforce.com/' + oppId; 
} 
else{ 
alert('Record creation failed - please notify system administrator'); 
}

The bold, italicized area is where the error is. The error message is:
<span class="errorStyle">Error: Field Record_Type_3__c does not exist. Check spelling.</span>

Record Type 3 does exist, and the spelling is correct. Is there someplace else that I need to define the "Record_Type_3" field? Thanks.