I get the same error in F10 x86_64. Weird, because it works fine on my F7 system. I don't know if it has anything to do with the installed versions of Tcl/Tk (F10 comes with 8.5.3 while F7 has 8.4.13), since Source Navigator seems to use its own internal version (8.3.2).
Anyway, I got it working on my F10 system by doing the following:
- comment out lines 182-184 in the file /opt/sourcenav/share/tk8.3/listbox.tcl
- comment out lines 457-459 in the file /opt/sourcenav/share/tk8.3/text.tcl
The mousewheel binding syntax there seems to be the problem. The mousewheel will still work in Source Navigator (I just tested it to make sure).