When is an error not an error?

[Michael Pokraka]

Hi all,
I have a bit of a troublesome situation:
Two steps, a user decision followed by a background task.
User executes item, and bg task fails due to binging/object issues. The
problem itself is another topic, but the most troublesome part is that
the WF remains in status 'In Process'!
 
In more detail:
Decision step logs look normal, ending with 'WI processing complete';
status 'COMPLETED'.
The next step does not appear in the log, but a red light appears in the
tech log with a message. No subsequent steps, nada. The only 'In
process' item on the whole log is the WF itself.
SWI2_DIAG doesn't show this up, which is why it's worrying.
The error is due to an uninstantiated object (resulting from a document
without line items) "Object 0 does not exist", "Syntax error in
expression" etc. I've no problem solving these, but more concerned about
other WF's in production.
 
Any input appreciated.
Cheers
Mike