PDF Creator Stopped

I have create a couple of session for generate PDF file, sometimes the PDF creator prompt below error and stopped all progressing. Please kindly help to fix. Thank you.

2016-02-23 10:42:10.1286 [Error] pdfforge.PDFCreator.App.Application_DispatcherUnhandledException: Uncaught exception in WPF thread System.ApplicationException: Object synchronization method was called from an unsynchronized block of code.
   at System.Threading.Mutex.ReleaseMutex()
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)