For one, why are you using a -pre version, when 1.0.2 is since long released?!
Then, unless you are 100% sure you know what you're doing, I would recommend dropping the "uri" parameter from the library entry. This can only work if you run the app from a web server (which is not recommended for source versions anyway). Are you sure this URI resolves to the correct path during run time? The default URI construction of the generator is usually fine and does what you want. If you can run your app from a file:// URL, you should rely on that.
Is the contrib downloaded correctly? Do you get warnings when the generator tries to access it online? There were issues with Sourceforge changing their ViewVC frontend (see this bug for a patch for this).
Can you check your download cache?! On Linux it's usually under /tmp/cache/downloads (You can use generate.py source -w to get a verbose logging of your job settings; scan for 'cache': {...'downloads':...} under the heading >>> Expanded job config: to find the path on your file system).
If you are in doubt if the contrib is downloaded correctly, download it from Sourceforge directly (look for "Download GNU tarball"). Put it in a suitable path on your file system and just adapt the "manifest" parameter of the library entry to point to the local Manifest.json (relative paths work best).
What do you get?