I am trying to customize the email opt out app in order to update a custom field HasOptOutCampaign__c which has been created on both the lead and contact objects.  Everything appears to be correct and I did not receive any error when saving this code but when I try to create an email service I receive the following error message:

• The Apex Class selected is not valid. An Apex Class that implements the Messaging.InboundEmailHandler interface must be selected.

Does anyone know how I might be able to correct this?  I will paste the code below.

Thanks so much.

Global class optOutCampaign implements Messaging.inboundEmailHandler{

Global Messaging.InboundEmailResult handleInboundEmail(Messaging.InboundEmail email,
                            Messaging.InboundEnvelope env ) {

// Create an inboundEmailResult object for returning
//the result of the Apex Email Service
Messaging.InboundEmailResult result = new Messaging.InboundEmailResult();
 
// Contact and Lead lists to hold all the updated records
List<Contact> lc = new List <contact>();
List<Lead> ll = new List <lead>();
 
// Convert the subject line to lower case, so I can match on lower case
String mySubject = email.subject.toLowerCase();
// String I am searching for in the subject line
String s = 'campaign opt out';
 
// Check variable to see if the words "campaign opt out" were found in the subject line
Boolean unsubMe;
// Look for the unsubcribe word in the subject line,
// if it is found return true, otherwise false is returned
unsubMe = mySubject.contains(s);
 
 // If unsubscribe is found in the subject line enter the if statement
 
 if (unsubMe == true) {
    
    try {
        
    // Lookup all contacts with a matching email address
        
     for (Contact c : [Select Id, Name, Email, HasOptOutCampaign__c
                        From Contact
                        Where Email = :env.fromAddress
                        And HasOptOutCampaign__c = false
                        Limit 100]) {
                        
        // Add all the contacts into the List   
                            c.HasOptOutCampaign__c = true;
                            lc.add(c);                                 
    }    
        // update all the Contact records
        
        update lc;
            }
    catch (System.QueryException e) {
        System.debug('Contact Query Issue: ' + e);
        }   

    try {
        // Lookup all leads matching the email address
     for (Lead l : [Select Id, Name, Email, HasOptOutCampaign__c
                        From Lead
                        Where Email = :env.fromAddress
                        And isConverted = false
                        And HasOptOutCampaign__c = false
                        Limit 100]) {
        // Add all the leads to the List        
        l.HasOptOutCampaign__c = true;
        ll.add(l);
                               
           System.debug('Lead Object: ' + l);   
    }    
        // Update all Lead records in the query
        update ll;
            }

    catch (System.QueryException e) {
        System.debug('Lead Query Issue: ' + e);
        }   

    System.debug('Found the campaign opt out word in the subject line.');
 }
 else {
    System.debug('No Campaign Opt out word found in the subject line.' );
 }
// Return true and exit
// True will confirm it is complete and no bounced email
// should be send the sender of the unsubscribe request.
result.success = true;
return result;
    }   
    
    // Test method to ensure you have enough code coverage
    // Have created two methods, one that does the testing
    // with a valid "unsubcribe" in the subject line
    // and one the does not contain "unsubscribe" in the
    // subject line
    
static testMethod void testoptoutcampaign() {

// Create a new email and envelope object
   Messaging.InboundEmail email = new Messaging.InboundEmail() ;
   Messaging.InboundEnvelope env    = new Messaging.InboundEnvelope();

// Create a new test Lead and insert it in the Test Method        
   Lead l = new lead(firstName='Rasmus',
            lastName='Mencke',
            Company='Salesforce',
            Email='rmencke@salesforce.com',
            HasOptOutCampaign__c=false);
   insert l;

// Create a new test Contact and insert it in the Test Method  
   Contact c = new Contact(firstName='Rasmus',
                lastName='Mencke',
                Email='rmencke@salesforce.com',
                HasOptOutCampaign__c=false);
   insert c;
   
   // test with subject that matches the unsubscribe statement
   email.subject = 'test campaign opt out test';
   env.fromAddress = 'rmencke@salesforce.com';
   
   // call the class and test it with the data in the testMethod
   optoutcampaign optoutcampaignObj = new optoutcampaign();
   optoutcampaignObj.handleInboundEmail(email, env );
                        
   }
 
static testMethod void testUnsubscribe2() {

// Create a new email and envelope object
   Messaging.InboundEmail email = new Messaging.InboundEmail();
   Messaging.InboundEnvelope env = new Messaging.InboundEnvelope();

// Create a new test Lead and insert it in the Test Method        
   Lead l = new lead(firstName='Rasmus',
            lastName='Mencke',
            Company='Salesforce',
            Email='rmencke@salesforce.com',
            HasOptOutCampaign__c=false);
   insert l;

// Create a new test Contact and insert it in the Test Method    
   Contact c = new Contact(firstName='Rasmus',
                lastName='Mencke',
                Email='rmencke@salesforce.com',
                HasOptOutCampaign__c=false);
   insert c;
   
   // Test with a subject that does Not contain campaign opt out
   email.subject = 'test';
   env.fromAddress = 'rmencke@salesforce.com';

   // call the class and test it with the data in the testMethod
   optoutcampaign optoutcampaignObj = new optoutcampaign();
   optoutcampaignObj.handleInboundEmail (email, env);                      
   }    
   
}