I am getting this error and I am unable to figure out why:

System.Xml.XmlException: You must write an attribute 'type'='object' after writing the attribute with local name '__type'.

Stack Trace: 

[XmlException: You must write an attribute 'type'='object' after writing the attribute with local name '__type'.]
   System.Web.Http.WebHost.HttpControllerHandler.EndProcessRequest(IAsyncResult result) +27904
   System.Web.Http.WebHost.HttpControllerHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +10
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8971341
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

This is the controller which I made request against:

public class CategoryController : ApiController {

        public IQueryable<Category> Get() {

            var dbContext = new ListItCheckItContext();

            return dbContext.Categories.AsQueryable();
        }
    }