I am trying to use the "Delete part" tool on a shapefile. While I am starting to use it, an error message shows up : "Could not snap segment. Have you set the tolerance in Settings > Project Properties > General?". I tried to set different tolerances in the snapping options, the error still shows up and I can't delete any part of my polygon. How to fix that?
I use QGis 1.8.0-Lisboa and Windows 7.