display correct error message on file uploads

www/manager/storage/ContentView.js

@@ -269,7 +269,10 @@ Ext.define('PVE.storage.Upload', {
 			me.close();
 		    } else {  
 			var msg = "Error " + xhr.status.toString() + ": " + Ext.htmlEncode(xhr.statusText);
-			Ext.Msg.alert(gettext('Error'), msg, function(btn) {
+			var result = Ext.decode(xhr.responseText);
+			result.message = msg;
+			var htmlStatus = PVE.Utils.extractRequestError(result, true);
+			Ext.Msg.alert(gettext('Error'), htmlStatus, function(btn) {
 			    me.close();
 			});