I'm trying to add the orderby expression on the fly. But when the query below is executed I get the following exception:

System.NotSupportedException: Unable to create a constant value of type 'Closure type'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

The strange thing is, I am query exactly those primitive types only.

string sortBy = HttpContext.Current.Request.QueryString["sidx"];
ParameterExpression prm = Expression.Parameter(typeof(buskerPosting), "posting");
Expression orderByProperty = Expression.Property(prm, sortBy);

// get the paged records
IQueryable<PostingListItemDto> query =
   (from posting in be.buskerPosting
    where posting.buskerAccount.cmsMember.nodeId == m.Id
    orderby orderByProperty
    //orderby posting.Created 
    select new PostingListItemDto { Set = posting }).Skip<PostingListItemDto>((page -   1) * pageSize).Take<PostingListItemDto>(pageSize);

Hope somebody can shed some light on this!