BPMN2 has a lot of different types, like user task, business rule task, etc. You you can also define generic tasks (they show up as <task> in your XML), but they have no execution semantics. It seems that the example you are trying to import is using such a generic task, this would prevent the process to be built. It might be worth verifying in designer if all the tasks in your process are morphed into a specific task (like user task etc.), they should have an icon if they are, if not you can still morph them in designer itself.
So this seems to be an issue with the process XML you are trying to import, not the import functionality itself.