It’s not about saving the project, it’s about saving a file to the render queue… Here is an excerpt of the code I use…
I’m copying a bit more of the script we need, as far I can tell, only the first 2 lines are relevant
var dir = new Folder();
var newLocation = dir.saveDlg("Select a render output folder..." );
if (newLocation != null)
{
if (myShow1_1.property("sourceText").value != "")
{
HeightWidth(myComp1);
app.project.renderQueue.items.add(myComp1);
var renderIndex = app.project.renderQueue.numItems; //count the items
var qItem = app.project.renderQueue.item(renderIndex);
qItem.outputModules[1].applyTemplate("QuicktimeAnimationAlphaHD");
var curOM = qItem.outputModules[1];
curOM.file = new File(newLocation.path + "/BL_" + String(myShow1_1.property("sourceText").value)+ "_" + String(myShow1_2.property("sourceText").value) + "_" + String(myTime1_1.property("sourceText").value) + ".mov"); //rename file
}