Exception Handling

[Peggy Stammler]

How can I raise an exception (error) in the Workflow?
 
I have a function module with exception 1 - ITEM NOT FOUND and 2 - ITEM
ERRONEOUS and 3 - OTHERS. This fm I call in my object type method. Here I
added these exceptions as well. Then I call this method in my task. Here I
see no possibility to define/link/.. these exceptions.
 
Can anybody help?
 
Thanks
Peggy