Try to use SVG render with IE9 and get an error: "Your browser does not support vector rendering".<div>OpenLayers breaks on 558 line of addFeatures method in Vector.js file: "this.renderer.locked = true;" - is null or undefined.</div>
<div>The way I use for adding layer:</div><div> var geojson_format = new OpenLayers.Format.GeoJSON();</div><div> map_vector_layer = new OpenLayers.Layer.Vector("", {styleMap: sm, rendererOptions: {zIndexing: true}});</div>
<div> map.addLayer(map_vector_layer);</div><div> map_vector_layer.addFeatures(geojson_format.read(regions));</div>