I use the TeaCommerce Starter Kit. If I'm in the last cart step and go to the productpage to add another products in the new empty cart, I can't add products to cart. If I click on the "add to cart"-Button I get the following error message:

Cart Error: 
<error><![CDATA[MESSAGE:
Ein Aufrufziel hat einen Ausnahmefehler verursacht.

STACKTRACE:
   bei System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner)

   bei System.RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner)

   bei System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)

   bei System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

   bei TeaCommerce.Presentation.TeaCommerceBase.RequestModule.invokeMethod(restExtension myExtension, Object[] paras)

INNEREXCEPTION:
System.InvalidOperationException: Das Objekt mit Nullwert muss einen Wert haben.

   bei System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)

   bei TeaCommerce.SessionController.get_CurrentOrder()

   bei TeaCommerce.SessionController.CheckCurrentOrderPaymentStatus()

   bei TeaCommerce.Base.AddOrderLine(Int32 nodeId, Nullable`1 orderLineId, Decimal quantity, Boolean isUnique)

   bei TeaCommerce.Base.AddOrderLine(Int32 nodeId, Decimal quantity)]]></error>

If I click on the "ok"-Button and click on the "add to cart"-Button again, it works and add the product to the cart.

Has anyone an idea to solve this error?

Best regards

Sören