I can't tell you about the problem itself, but you can maybe do a workaround running nona from the command line on the PTO file created. To generate the final mounted panorama you could open a command line window, go to the folder where the project is:
> cd /folder/of/the/project
and then:
> nona -o output project.pto
and then:
> enblend -o final.jpg -w output*.tif
Just tell me if you don't understand anything about command line, nor even how to open it, so I can explain in more details (you can also try to search something on google).
Running on the command line can also help us to see if the problem involves some of these tools, which Hugin uses behind it. If they are the problem (but I don't think they are) we will probably have some error message that could give us some more hints.
Oh, I've just remembered another possible workaround. You can disable "Batch Processor" as the tool used to render the final panorama in the Preferences. Just go to the "Stitcher" tab and change "Batch processor" to hugin_stitch_project under the Processor option. I always do this by the way.
Cheers,