A problem assignment, or an assignment in error, is an assignment that remains open for a long time or references a work object or rule that is no longer available. When either of these conditions is detected, the assignment status (the Assign-.pyAssignmentStatus property) is changed to Error.
Problem assignments require review and analysis. To research problem assignments, use the reports that are available from Designer Studio > Process & Rules > Tools > Work Admin > Worklist Assignment Errors.