qgis - "Node tool: could not snap to a segment on the current layer" message

I have a strange issue. Editing a layer with node tool I get always the following message: "Node tool: could not snap to a segment on the current layer." This error happens to me even with a fresh install of new 2.6 version only on my xp system (erased .qgis directory in profile and with no plugin at all) I get this error in all the currently installed release (2.0, 2.2, 2.4, 2.5 weekly, 2.6) and appears to be system dependant as other xp systems near to me are not affected. What can I do?

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