Resolution:
In BW, you can design a top-level process as following:

                   |-----------------------------------------------------|
                   |                                                                      |
   start------|----activity1----callProcessActivity----|--------end
     |             |                                                                      |             |
     |             -----------------------------------------------------|              |
    error                                         |                                                 |
   transition                            group                                            |
     |                                   error transition                                   |
     |                                                |                                                 |
      ------------------------------------|                                                 |
                                                handle                                          |
                                                   error --------------------------------

This means that any error that is unhandled within the scope of the group plus errors thrown by start activity will be handled by 'handle error' activity. Since scope of the group includes a call process activity, any unhandled errors in the sub process (assuming it does not spawn a sub job) will also be caught.

Attached is an example which demonstrates this.

IM has a error task that can be dropped in the top-level process. This acts as a catch all for any unhandled errors in the job even if its in sub-processes. How does one achieve something similar in BW? [ Global Error Handler ]