this is not working with the latest version of inkscape.

[extorn]

I've updated the file as best I can though I'm not a python developer. It does work now, but still warns of a deprecated API use that I cannot solve. Hopefully you can accept these changes and fix the remaining issue.

rounded_corners.py.txt

[monomon]

Fixed now, thanks for bringing it to my attention.
Haven't updated it in the Inkscape gallery yet, due to difficulties logging in.