AmbiguousMatchException - where to look?

I have a ton of working objects in a WinRT app and have followed the same pattern for all of them. But with a new one I've created, I get the following exception when executing an async Fetch method on a list object.

System.Reflection.AmbiguousMatchException

This occurs when I try to do this:

        public static async Task<ProductCategorySalesInfoList> GetListAsync()
        {
               return await DataPortal.FetchAsync<ProductCategorySalesInfoList>();
        } 

I feel like I've probably missed something somewhere, but can't seem to find it. The stack trace for the inner error of the ErrorInfo object is as follows. Any ideas on where to look or what to look for? Thanks.

   at System.RuntimeType.GetMethodImpl(String name, BindingFlags bindingAttr, Binder binder, CallingConventions callConv, Type[] types, ParameterModifier[] modifiers)   at System.Type.GetMethod(String name, BindingFlags bindingAttr)   at Csla.Reflection.MethodCaller.GetMethod(Type objectType, String method, Boolean hasParameters, Object[] parameters)   at Csla.Reflection.MethodCaller.GetMethod(Type objectType, String method, Object[] parameters)   at Csla.Server.DataPortalMethodCache.GetMethodInfo(Type objectType, String methodName, Object[] parameters)   at Csla.Server.DataPortalMethodCache.GetFetchMethod(Type objectType, Object criteria)   at Csla.DataPortal'1.<DoFetchAsync>d__11.MoveNext()--- End of stack trace from previous location where exception was thrown ---   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)   at System.Runtime.CompilerServices.TaskAwaiter'1.GetResult()   at Csla.DataPortal'1.<FetchAsync>d__1b.MoveNext()--- End of stack trace from previous location where exception was thrown ---   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)   at System.Runtime.CompilerServices.TaskAwaiter'1.GetResult()   at Csla.DataPortal.<FetchAsync>d__c'1.MoveNext()