Generic decision Task and ABAP OO

I have implemented a workflow using ABAP OO, which has a couple of user decision steps.

Now I have made a copy of the generic decision task (8247) into my own custom task. I then copied over the code from the process method of the DECISION BO into my own custom BO. I then referenced the custom BO in my custom task. I tied this custom task to a user decision step in my workflow.

code

I had to this so that I could extend the functionality of the code to do something specific to my logic. This works fine.

However when I write the same code in a method of my ABAP class and tie it to the same custom task instead of the BO, the workflow complains while activating "TASK XXXXX cannot be used as a decision task".

Any advice would be greatly appreciated. Thanks a lot in advance.