Anyone see the error in the test method below?  The thing compiles fine but I see a bug in it that is the error "cannot modifu a list while it's being iterated"

Annoying thing is I did this last week but forgot how I resolved this.  It's obvious I just don't see it.  Anyone see what's wrong with this code?

Thanks

	static testMethod void testEngagementsCreatedByOppUpdate()
        {

             Account acct = new Account(name='test account');              
             insert acct;
		
	     Opportunity[] oppsToCreate2 = new Opportunity[]{};
		
                 for(Integer x=0; x<200;x++)
                 {
		      Opportunity opp = new Opportunity();
                      opp.AccountId=acct.Id;
                      opp.Name = 'Test'+x;
                      opp.Probability = 10;   
                      opp.Type = 'Trial';
                      opp.CloseDate = System.Today();
                      opp.Region__c = 'East';
                      opp.Territory__c = 'BE South';
                      opp.LeadSource = 'Chat';
                      opp.StageName = 'Evaluating';
                      opp.License_type__c = 'Subscription';
                      opp.Forecasted_Amount__c = 1;
                      opp.ELA__c = 'No';
                      opp.Services_Use_Case__c = 'test text'+x;
                      opp.Work_Location__c = 'Onsite';
                      opp.Size_of_Deal__c = '0-25K';
                      opp.Services_Planned__c = 'Client Services';
                      opp.Customer_s_Expected_Start_Date__c = 'This month';
                      opp.Expected_Services_Work_Hours__c = '5-10 hours';
                      opp.Term__c = 1;
		      oppsToCreate2.add(opp);
		 
		}

		insert oppsToCreate2;

               for(Opportunity opp: oppsToCreate2)
               {
                  opp.Probability=80;
                  opp.Services_to_be_Delivered_by__c = 'Training Team';
                  oppsToCreate2.add(opp);
               }
 
                update oppsToCreate2;

                List< SFL5_Projects__c > insertedEngagements2 = [SELECT Name, Id
                                      FROM SFL5_Projects__c 
                                      WHERE Opportunity__c IN :oppsToCreate2];
              
                Integer size2 = insertedEngagements2.size();
                system.assertEquals(200,size2);   		   
		Test.stopTest();	

	}