Summary
ObjectNodes connected by ObjectFlows must have the same upper bounds.
Details
ObjectNodes connected by an ObjectFlow, with optionally intervening ControlNodes, must have the same upper boundaries.
Tips
When you get an R1300 warning on an ObjectFlow, verify that all upstream and downstream ObjectNodes of this flow have the same upper boundaries. The upper boundaries of an ObjectNode can be changed through the "Element" view when the ObjectNode in question is selected.