How can I reference a field from the Campaign Member object?

Question

I´m trying to create an editable related list for Campaign Members, but can´t seem to reference a field (in my extension below) from the actual Campaign Member object (Description__c). I get a "No such column 'Description__c' on entity 'CampaignMember'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name" error within the Developer Console.

Which means it can´t be displayed in the visualforce page (the code "works", but instead of appearing as a table, it appears as an "SObject row was retrieved via SOQL without querying the requested field" error). Any ideas?

   public with sharing class CampaignRelatedListExtension
{
    public List<CampaignMember> campaignMembers { get; private set; }
    public CampaignRelatedListExtension(ApexPages.StandardController controller)
    {
        campaignMembers = [
            SELECT Campaign.Name, Campaign.Startdate, Campaign.Type, Description__c FROM CampaignMember
            WHERE ContactId = :controller.getId()

        ];  
}
 }   

And my vf page:

<apex:page standardController="Contact" extensions="CampaignRelatedListExtension">
 <apex:form >
    <apex:pageBlock title="Campaign Members">
        <apex:pageBlockTable value="{!campaignMembers}" var="member">
            <apex:column value="{!member.Campaign.Name}" />
            <apex:column value="{!member.Campaign.Startdate}" />
            <apex:column value="{!member.Campaign.Type}" />
            <apex:column value="{!member.Description__c}" />
                    </apex:pageBlockTable> 
    </apex:pageBlock>
 </apex:form> 
</apex:page>

Answer 1

As it turns out, there was no problem with my code. The problem was that I hadn´t refreshed my sandbox; the Description__c field (which I created recently) wasn´t recognized as a field belonging to the Campaign Member object, because as far as the sandbox knew, it didn´t even exist.

Thanks for your help, @Adrian Larson and @Mauricio Oliveira.