Using the standard 'create invoice from salesorder' in workflows

[Guido1982]

I've tested with my test file again, but still I can manually create an invoice from a salesorder, but I can't get the product lines accross in the actual workflow. Weird thing is that if I copy the example in this file I get a fatal error because 'doTask' does not comply with the parent class or interface. I can solve this by passing in the argument by reference like here but I don't understand why other workflows don't have to do this.

Maybe this has something to do with the productlines not being copied.