Can't Convert MS Project mpp


We have a VB6 application which uses the PDFCreator com interface to convert various files to pdf

There are no problems converting MS Office, .txt .msg files but when I try to convert a .mpp file PDFCreator starts, the MS Project file opens but nothing happens. Only when I manually close the mpp file will PDFCreator close as programmed

With pdfJob
 .cOption("AutoSaveDirectory") = sTargetPath
 .cOption("AutoSaveFilename") = sTargetFileName  
 'If .cIsConverted = True Then                      
  .cPrintFile (sSourceFile)                     
'gets stuck here                
  .cPrinterStop = False

I can open the MS Project file manually and print to the PDFCreator printer without any problems

Thanks in advance