Quoting Ralf Stephan <ralf@...748...>:
(which is very cryptic)
Sadly that's par for the course with C++ errors.
I have looked in gc-managed.h but didn't find a thing about it.
The error is a C++ issue rather than anything specific to the Inkscape::GC APIs. One base class (Gtk::Window in this case) is hiding the custom new and delete operators introduced by another base class (in this case GC::Managed).
In general when you see a message like:
somefile.cpp: In [function a]: someotherfile.h: error: [member function] is inaccessible somefile.cpp:[line number]: error: within this context
It means the code (at somefile.cpp:[line number]) is trying to access a protected or private member function as if it were public.
If the member function is in fact declared as public, then it is likely being hidden by an interaction between different base classes.
-mental