Daniel - Sydney (Glad I'm not in Townsville)
It used to be my favourite place in the world.
When an engine is missing from the Trainset and that engine is listed as the lead in a consist the OR Menu displays "Load error" in the Engine selection box. So one could assume when the OR Menu lists "Load Error" in the Activity selection something that the Activity calls is not in the correct location such as a Path or Service file. Suggest that the OP open the Activity and verify that all the Paths and services called by the activity are present in their respective folder.
Charles