workflow task not started

[Gordy, Lynn L.]

We are in the processes of upgrading from 3.0f to 4.6c.  For our inbound
orders we have a custom single step task cloned from the SAP task 8086.
Intermittenly when the idoc encounters an application error (status 51) it
does not show up in the inbox.  When I look for the workitem it does not
exist anywhere.  If I run the task manually (SWUS) then it shows up in the
inbox.   Any ideas?