ENV: mapguide opensource 2.0.1 + mapguide studio 2009 + visual studio 2005(c#)

i want to delete the features in a layer ,i use the follow lines:
        MgDeleteFeatures deleteCmd = new <b>MgDeleteFeatures</b>(featureName, "KEY >= 0");
        MgFeatureCommandCollection commands = new MgFeatureCommandCollection();
        commands.Add(deleteCmd);
        featureService.<b>UpdateFeatures</b>(dataSourceId, commands, false);

but it throw an exception:
<font color=red>
"Please try your operation later as the resource was busy: Session:287d258c-0000-1000-8000-005056c00001_zh_7F0000010AFC0AFB0AFA//Line.FeatureSource"          </font>

before i do the delete command with UpdateFeatures(),i do a selection operation:
...
        MgResourceIdentifier resId = new MgResourceIdentifier(layer.GetFeatureSourceId());
        MgFeatureQueryOptions queryOption = new MgFeatureQueryOptions();
        queryOption.SetFilter(queryString);
        MgFeatureReader featureReader = featureService.SelectFeatures(resId, queryLayer, queryOption);
        MgSelection selection = new MgSelection(map);
        selection.AddFeatures(layer, featureReader, 0);
        selectionXML = selection.ToXml();
        selection.Save(resService, map_name);   
-----------------------------------------------------------------------------------------

my question is how to clear selection or disselect at server ,before i delete the features???


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