AsEnumerable returns value, filter options does not

Question

AsEnumerable returns a value but without it returns not a value.

I seem to have an issue with extracting a certain value from my odataQueryservice.

        ODataQueryService ax = new ODataQueryService(new Uri(Link));

        double test = double.NaN;
        try
        {
            test = ax.InventTable.Where(X => X.InventTable_ItemId == "030001").Select(x => x.InventTable_Width).FirstOrDefault();
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }

Returns an error:

System.Data.Services.Client.DataServiceQueryException: An error occurred while processing this request. ---> System.Data.Services.Client.DataServiceClientException: <?xml version="1.0" encoding="utf-8" standalone="yes"?>
<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <code></code>
  <message xml:lang="da-DK">An error occurred while processing this request.</message>
</error>
   at System.Data.Services.Client.QueryResult.ExecuteQuery()
   at System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents)
   --- End of inner exception stack trace ---
   at System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents)
   at System.Data.Services.Client.DataServiceQuery`1.Execute()
   at System.Data.Services.Client.DataServiceQuery`1.GetEnumerator()
   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
   at System.Data.Services.Client.DataServiceQueryProvider.ReturnSingleton[TElement](Expression expression)
   at System.Data.Services.Client.DataServiceQueryProvider.Execute[TResult](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)

but this

        ODataQueryService ax = new ODataQueryService(new Uri(Link));

        double test = double.NaN;
        try
        {
            test = ax.InventTable.AsEnumerable.Where(X => X.InventTable_ItemId == "030001").Select(x => x.InventTable_Width).FirstOrDefault();
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }

returns the actual value, but loads the entire table... Someway to avoid this, or why am I getting the first error in the first place?