I have a created a VF Page that supposed to replace the activity history section in the contact page layout related list. Although I can see it in the page layout, it won't let me add it to the related list section.

public class ActivityController {
    private final Contact cont;

    public ActivityController (ApexPages.StandardController stdController) {
        this.cont = (Contact)stdController.getRecord();
}

    public PageReference newTaskforCall()
    {
        PageReference NewTaskPage = new PageReference('/00T/e?title=Call&who.id=' + System.currentPageReference().getParameters().get('id') + '&followup=1&tsk5=Call&retURL=%2F003R000000ArDZn');
        NewTaskPage.setRedirect(true);
        return NewTaskPage;
    }


    public String hasNext { get; set; }

    public PageReference next()
    {
        return null;
    }


    public String getHasPrevious()
    {
        return null;
    }


    public PageReference previous()
    {
        return null;
    }

        Public Task[] getActivities()
        {
                return [Select id, subject, what.name,activitydate, owner.name, lastmodifieddate from Task where whoid = :System.currentPageReference().getParameters().get('id') and calldurationinseconds > 0];
        }

        public Contact getContact()
        {
                return [Select id, name
                        from Contact where id = :System.currentPageReference().getParameters().get('id')];


        }
}

   

<apex:page standardController="Contact" extensions="ActivityController" tabstyle="Contact" sidebar="false">

  <apex:form id="myform">

    <apex:pageBlock title="Cal History" >

    <apex:pageblockButtons >

    <apex:commandButton value="Log Call" action="{!newTaskforCall}">

    </apex:commandButton>

    </apex:pageblockButtons>

    <apex:pageBlockSection title="" columns="5" collapsible="true">

    <apex:panelGrid columns="2" id="navigation">

    </apex:panelGrid>

    <apex:dataTable value="{!Activities}" var="each" border="0" styleClass="list">

        <apex:column headerValue="Subject"><a href="/{!each.id}">{!each.subject}</a></apex:column>

        <apex:column headerValue="Related To"><a href="/{!each.what.Name}">{!each.what.Name}</a></apex:column>

         <apex:column headerValue="CSD"><a href="/{!each.owner.id}">{!each.owner.Name}</a></apex:column>

        <apex:column headerValue="Due Date">{!each.ActivityDate}</apex:column>

        <apex:column headerValue="Last Modified Date/Time">{!each.lastmodifieddate}</apex:column>

    </apex:dataTable>

    </apex:pageBlockSection>

    </apex:pageBlock>

  </apex:form>

</apex:page>