Hi,
I'm new to the SF Apex triggers, and I am following this manual (https://help.salesforce.com/articleView?id=entitlements_milestones_trigger.htm&type=5) to enable Auto-Complete Case Milestones.
I managed to add create the first two Apex classes and the first Apex case trigger (Sample Trigger 1), but when I try to insert the third code (Sample Trigger 2, embedded below), I get the following error:
Error: Compile Error: Incorrect SObject type: EmailMessage should be Case at line -1 column -1

I tried looking online for a solution, but could'nt find any.
Does anyone have an idea how to solve this issue?
Thanks!
 

trigger CompleteFirstResponseEmail on EmailMessage (after insert) {
    if (UserInfo.getUserType() == 'Standard'){
        DateTime completionDate = System.now();
        Map<Id, String> emIds = new Map<Id, String>();
        for (EmailMessage em : Trigger.new){
            if(em.Incoming == false)
                emIds.put(em.ParentId, em.ToAddress);
        }
        if (emIds.isEmpty() == false){
            Set <Id> emCaseIds = new Set<Id>();
            emCaseIds = emIds.keySet();
                List<Case> caseList = [Select c.Id, c.ContactId, c.Contact.Email,
                    c.OwnerId, c.Status,
                    c.EntitlementId,
                    c.SlaStartDate, c.SlaExitDate
                    From Case c where c.Id IN :emCaseIds];
            if (caseList.isEmpty()==false){
                    List<Id> updateCases = new List<Id>();
                    for (Case caseObj:caseList) {
                        if ((emIds.get(caseObj.Id)==caseObj.Contact.Email)&&
                            (caseObj.Status == 'In Progress')&&
                            (caseObj.EntitlementId != null)&&
                            (caseObj.SlaStartDate <= completionDate)&&
                            (caseObj.SlaStartDate != null)&&
                            (caseObj.SlaExitDate == null))
                                updateCases.add(caseObj.Id);
                    }
                    if(updateCases.isEmpty() == false)
                        milestoneUtils.completeMilestone(updateCases, 
                                'First Response', completionDate);
            }
        }
    }        
}