'System.ServiceModel.FaultException`1' when using RetrieveMultiple with FetchXML in Dynamics CRM

Question

I am consistently getting the above error when attempting to get results from a FetchXML query. Any help would be appreciated. The error always occurs on the line:

    EntityCollection GetAllOpenActivitiesXML_result = service.RetrieveMultiple(fetched1);

Here is the rest of the code:

ITracingService tracingService = executionContext.GetExtension<ITracingService>();
IWorkflowContext context = executionContext.GetExtension<IWorkflowContext>();
IOrganizationServiceFactory serviceFactory = executionContext.GetExtension<IOrganizationServiceFactory>();
IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);

Entity opp = new Entity("opportunity");
opp.Id = context.PrimaryEntityId;

string GetAllOpenActivitiesXML = @"
<fetch distinct='false' mapping='logical' aggregate='true'> 
<entity name='activitypointer'>
     <attribute name='activityid' aggregate='count' alias='activityid'/>
          <filter type='and'>
                 <condition attribute='statecode' operator='eq' value='0' /> 
          </filter>
     <link-entity name='opportunity' from='opportunityid' to='regardingobjectid'>
          <filter type='and'>
                 <condition attribute='name' operator='eq' value='MyOpportunity' />
          </filter>
     </link-entity> 
 </entity> 
 </fetch>";

    try {
         FetchExpression fetched1 = new FetchExpression(GetAllOpenActivitiesXML);
        EntityCollection GetAllOpenActivitiesXML_result = service.RetrieveMultiple(fetched1);

             foreach (var c in GetAllOpenActivitiesXML_result.Entities)
             { 
              Int32 totalOpenActivities = (Int32)((AliasedValue)c["activityid"]).Value;
              opp["new_openactivities"] = totalOpenActivities;
              }
        }
    catch { 
           opp["new_openactivities"] = 0; 
          }

 service.Update(opp);

Answer 1

The issue is caused because you're using the name of the field as alias so if you change the alias it will start working:

<fetch distinct="false" mapping="logical" aggregate="true" >
  <entity name="activitypointer" >
    <attribute name="activityid" alias="activityid_count" aggregate="count" />
    <filter type="and" >
      <condition attribute="statecode" operator="eq" value="0" />
    </filter>
    <link-entity name="opportunity" from="opportunityid" to="regardingobjectid" >
      <filter type="and" >
        <condition attribute="name" operator="eq" value="MyOpportunity" />
      </filter>
    </link-entity>
  </entity>
</fetch>

Also, I don't know which CRM version are you using but I'm pretty sure that this plugin can be replaced by a rollup field so I'd give it a try!