The picard based tools nicely infer a reference sequence, and still allow the user to override. However, this inference does not work in a workflow, since that select list has no value. I'm trying to come up with a clean way for the workflow logic to read the input dataset dbkeys, but I'm not sure whether I should do this in handle_unvalidated_param_values... That's where the error comes up, but I think there is probably a better place to do the lookup and avoid the error altogether. Any pointers? Brad -- Brad Langhorst langhorst@neb.com<mailto:langhorst@neb.com> 978-380-7564