Comment 10 for bug 186582

Also - the order in which the items are selected is important.

Unless you select the object first, even if it is already a path - you get the error.

See details from my report here:
https://bugs.launchpad.net/inkscape/+bug/168336

Has anyone tested the above patch? does that work? help?

Agree this is a usability issue. The application doesn't crash - but it's an ugly ugly error for a non-technical user.