I have tried again with the example doc. First time I tried to export the dialog became non responsive for a while. I clicked on it and it disappeared - but the program did not crash. So I tried again and was able to export the pdf. Tried my file and it also exported. I wonder if the the original freeze/ non responsiveness was the program reading the file list of the output directory but taking a long time to do so. Once it had read the files in the dir it worked OK. Sorry to have bothered you but it appears that it is now working OK and I know that eventually the dialog will "unfreeze".