Deleting all models from group

Hello!

I wanna delete all models from the selected group.

My code is:

function delFiles() {

     var gr = ArisData.getSelectedGroups()[0];

     Dialogs.MsgBox("Selected group: " + gr.Name(1049));

     var delModels=gr.ModelList(true);

     Dialogs.MsgBox("Number of models: " + delModels.length);    

     for(var i = 0; i < delModels.length; i++){

          Dialogs.MsgBox("Del status of" + delModels[i].Name(1049) + " model: " + gr.Delete(delModels[i]));

     }

}

function main() {

     delFiles();

}

main();

All models are closed. I can delete their manually.

But status of deleting of each model by script is "false".

Tell me please why I can not delete models from selected group.