"Catchpodderplugins" is not installed

What version of Ubuntu are you using? 64 bit or 32 bit?
What qmlscene command does Qtcreator generate? Is there a "-I /home/....../utouch/catchpodder/plugins" in it?

I'm using 64bit up-to-date raring.

I'm gonna check qmsscene command and catchpodder/plugins tonight.

Here is the complete output:

Starting /usr/lib/x86_64-linux-gnu/qt5/bin/qmlscene -I /home/....../utouch/catchpodder -I /usr/bin -I /usr/lib/x86_64-linux-gnu/qt5/qml -I /home/....../utouch/catchpodder/plugins /home/....../utouch/catchpodder/Catchpodder.qml
file:///home/....../utouch/catchpodder/Catchpodder.qml:166 Type PodcastController unavailable
file:///home/....../utouch/catchpodder/controllers/PodcastController.qml:24 module "Catchpodderplugins" is not installed

/usr/lib/x86_64-linux-gnu/qt5/bin/qmlscene exited with code 255

Indeed, the -I /home/....../utouch/catchpodder/plugins is present

ok. Then I guess the precompiled plugin just doesn't work for your system. But: you should be able to compile it yourself.
The code for the plugin is in the "filedownload" branch: https://code.launchpad.net/~djfun/catchpodder/filedownload
qmake && make or using Qt Creator (and then replace the .so file, I have yet to figure out, where exactly the plugin should be installed to)

It works, thanks !

PS: For my education , is it possible to have only one QtCreator Project with both QML & C++ ?