Is there a simple fix for this error?

From Fiddler response:

[NullReferenceException: Object reference not set to an instance of an object.]
SmartWebControls.SmartPrint.Web.SmartPrintHandler.ProcessRequest(HttpContext context) +596
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +598
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +170


This is all I'm doing, it worked once or twice and now gives me the above error:

PrintSettings ps = new PrintSettings();
ps.ElementsToPrint = new List<UIElement> { (UIElement) this };

SmartPrintManager printMgr = new SmartPrintManager();
printMgr.AutoGeneratePrintDocumentViewer = true;


printMgr.Print(ps);

Thanks.