Ubuntu Tweak Janitor crashes any time when scan for old kernels

[Venelin]

Distribution: Ubuntu 12.04
Application: Ubuntu Tweak 0.8.4-1~precise1
Desktop: ubuntu

I'm trying to delete the old kernels from my system via Ubuntu-Tweak, unfortunately any time I go to Janitor and check 'Old kernel' the application crashes during the scan.
The only time it didn't crash showed the following message:
"
Traceback: (most recent call last):
File "/usr/lib/python2.7/dist-packages/ubuntutweak/janitor/oldkernel...
self.emit('scan_finished, True, count, size)
TypeError: could not convert type long to (null) required for parameter 2
"

when I run from Terminal, I get the following:
sudo ubuntu-tweak
Backend : ini
Integration : true
Profile : default
Adding plugins
Initializing core options...done

(ubuntu-tweak:8017): Gtk-CRITICAL **: gtk_text_attributes_ref: assertion `values != NULL' failed

(ubuntu-tweak:8017): Gtk-CRITICAL **: gtk_text_attributes_ref: assertion `values != NULL' failed

(ubuntu-tweak:8017): Pango-CRITICAL **: pango_layout_new: assertion `context != NULL' failed