Hi. The paramenter name 'col' was changed to 'column' after 6.0.0 release in v.surf.idw: http://freegis.org/cgi-bin/viewcvs.cgi/grass6/vector/v.surf.idw/main.c.diff?r1=1.5&r2=1.6 This change has broken use of this module GRASS Tools in QGIS. Please don't change parameter name in at least 6.x release line. Thanks Radim