A: When there's a problem with a workflow, an error will often be written to the SCOM event log on the SCSM server. (Yes, it's the SCOM event log, because SCSM is built on SCOM).
For more detail on workflow errors, you can open the status of a workflow and see the statuses of its executions. Open the SCSM console and select the administration wunderbar, then open Workflows, Status. Select the workflow in question and you can see workflow instances that need attention—meaning they had a problem—or all instances. You can then select to view the log for that instance of the workflow and see details about which part failed and a more detailed error, as shown here.
This will, hopefully, help you ascertain the cause of the problem and fix it. You'll notice that you can also try to rerun the workflow or ignore the error.