What about all the other development objects related to the workflow and tasks? Example: Maybe some of the tasks uses a method that calls a function module X, and the function module X has not been transported to production. Or maybe your container element refers to Z-data element etc. Can you check all the possible Z-objects that your workflow might be using?
Can you open the template with SWDD? If you can, can you run the syntax check?
Regards,
Karri