PDFCreator Spool Not Responding

When I try to print with PDFprinter, I get the spooler panel that shows a backlog of files to be printed, with the most recent one on top. The print request goes through to create the PDF file, but the backlog in the PDFPrinter print queue remains, and the spooler then goes into 'not responding', requiring a forced shutdown by windows task manager. This only now started.

 

I have been running v 0.9.3 for a long time. The problem just appeared today. I upgraded to 1.1.2, and the same problem occurred.

How do I clear the queue?