I fairly new to GIS, and I'm having an issue with dissolving a vector. To start, I'm running QGIS 2.14.15 on Windows 7 Pro. When I try to dissolve the polygons it creates a blank shapefile. All of the files are in the same projections. I poked around and found Fixing geometry validity errors in QGIS? which lead me to finding two errors (see below).
187,Unknown geometry type 0;
187,Geometry has 1 errors.
221,Unknown geometry type 0;
221,Geometry has 1 errors.
When I select the an entry and try to Pan to selection it says "Geometry is Null". Running LWGEOM - Make Valid gives "[Error 87] The parameter is incorrect See log for more details", but there aren't any details in the log. Grass 7 v.clean runs and doesn't seem to do anything (not sure if I'm using it correctly).
Edit: The files are set to EPSG:3310. I used union to join two polygon layers showing range distribution. My dissolve process argument is ---Dissolve all---. When using the check geometry validity function on the union layer, I selected Save Error Location as a point shapefile, the file is empty. In LWGEOM I used the default setting. Using Grass v.clean I used cleaning tools snap, bpol, prune and rmarea. I systematically varied the threshold between 0.1 and 1000. In the advanced parameters varied v.in.ogr snap tolerance from -1.0 to 5. and the min area from 0.001 to 1000. They all give the same empty file.
Since my OP I tried using SAGA 2.3.2 => Vector Polygon Tools=> Polygon dissolve (all polygons). It will dissolve the layer but omits 5 polygons where data intersects.