||Thank you, you lead me to a good solution!
Using ET GeoWizards, I first converted my polylines to point (only nodes). After, I calculated the shortest distance from each point to the closest using a tool available on ESRI France (the shortest point distance within ET GeoWizards does not seem to work with a single layer). Then, all topologicaly correct nodes have a distance of 0 because they are exactly on the node of the next polyline... but all the remaining nodes with a shortest distance different than 0 reveal potentiel problems. Using the attribute table of the layer, I can zoom on each nodes presenting a problem and correct my data. Afterwards, all the polygons close proprely using ET GeoWizards. This techniques is maybe not the best but I can fix my data now.
Despite having done some VBA in the past, your sample code did not really work to spot the problems. Sorry! Also, somebody suggested using FME to detect such conflicts. And, the Clean Dangling Nodes on ET GeoWizards seems interesting but does not work with more than 100 features in the free edition.