Looks like there is bug report about pdfshuffler on freya :
Launchpad Bug Report
As for the error you are getting :
Gtk-Message: Failed to load module "pantheon-filechooser-module"
A bug report was filed and fixed. pantheon-filechooser-module-bug-report
You might have installed an older version of the application.
Try re-installing the application, but from this link:
pdfshuffler for ubuntu 14.04
Download the package according to your system architecture.
According to this post the user is having a similar problem with a different application, and updating the application to the latest one fixes the problem.
Now, if you are getting an error about not finding a package named poppler:
You need to install poppler python bindings, which will be pypoppler and pypdf(recently changed to pypdf2).
Ohh, and also remember, not to run pdfshuffler as root.
Reffer to these if you want a detailed answer to the poppler problem.
poppler not found solved
could not import pdfshuffler debian bug report
For a different approach to this problem, check if you are getting this error:
Gtk-Message: Failed to load module "canberra-gtk-module"
If you are, then you may find help here: failed to load cranberra-gtk-module
or here : cranberra-gtk-module solved
Now, for the other part of the problem,
I hope you will find help in either of these links. Both show how to make radio tray work in elementary:
Radio tray stopped working in freya
Radio tray not working
Hope these links might help you find what you need.