Topic: Generate JSON from Linq

I'm trying to create JSON from an object(including an object nested within this object) using LINQ.

The basic class structure is a collection of Attributes all contain a collection of AttributeItems.  From this i want to get the AttributeID (from Attributes) and AttributeItemsID/s (from AttributeItems) for each Attribute. 

The code i created is:
    Dim _attributes As IEnumerable = From attribute In oWebCategoryDisplay.Attributes() _
    Select AttributeId = attribute.AttributeItemId, _
    AttributeItems = (From items In attribute Select AttributeItem.AttributeItemId)

But i get the error:
Expression of type 'Object' is not queryable. Make sure you are not missing an assembly reference and/or namespace import for the LINQ provider.

If anyone could help me, that would great!!  Thanks in advance!