Error: "List has no rows for assignment to SObject"

The full error will look something like this:

"List has no rows for assignment to SObject
Error is in expression '{!initialize}' in component <apex:page> in page job_editAn unexpected error has occurred. Your development organization has been notified."

Whenever this happens, you want to double check two things:

Make sure that the client's account has a Primary Contact selected (there is a "Select Primary" button under the Contacts section is there is none selected)

Make sure there is a Contact listed on the Job Series (if not, you will need to add one by Editing the series, searching for the appropriate contact, then saving the series.  You will also most likely need to reset the series to make sure the change trickles down to the individual jobs)