Hello,
If I have understood correctly then workitems are being sent to Manager when they go into error.
You want to change this so that it goes to you instead. Normally this would be done in SWDC but you say that the Manager is not specified there.
Well, what is specified in SWDC? It could be your manager's Position or P number or Org Unit..
SWDC is the normal way of doing this.
The only other possibility I can think of is a batch job that's running and looking for workitems in error and forwarding them. Check SM37.
regards
Rick