I am attempting to update a custom field in both CampaignMember and in Contact. I have checked and rechecked, and the fields are identical, i.e. both are lookups related to opportunity - one with a child relationship to contact, the other with a child relationship to CampaignMember. 

However, I am getting the "FIELD_INTEGRITY_EXCEPTION, Opportunity: id value of incorrect type" only on the "update changeContact"

and it appears to me that it should be the same type as the "update changeCampaignMember" 

What am I missing? Code follows:

if (myLead.IsConverted == true && myLead.IsConverted != oldLead.IsConverted) {

   CampaignMember[] convertedCampaignMember = [SELECT CampaignMember.Id, CampaignMember.Opportunity__c  FROM CampaignMember  WHERE CampaignMember.Id = :myLead.ConvertedContactId LIMIT 1];

for (CampaignMember changeCampaignMember : convertedCampaignMember){              changeCampaignMember.Opportunity__c = myLead.ConvertedContactId;            

  update changeCampaignMember;            }            

Contact[] convertedContact = [SELECT Contact.Id, Contact.Opportunity__c  FROM Contact WHERE Contact.Id = :myLead.ConvertedContactId LIMIT 1];

// if (!convertedContact.isEmpty()){            

for (Contact changeContact : convertedContact){            

  changeContact.Opportunity__c = myLead.ConvertedContactId;            

  update changeContact;            }
// } }