A transaction or sub-transaction was opened but not closed

[rinacimareller]

Hi, this is my first post in the forum, so if i do something wrong, just tell me please.

I started studying Revit  API  and i trying to do a simple AddIn, just copy a element to a location that i select.

I wrote the code but when i try to run in Revit i get a error message.this is the first messageWhen i click on "Fechar" i get this

can someone help me please? 

this is the code i get:

namespace Lab1PlaceGroup
{
     [Transaction(TransactionMode.Manual)]
     [Regeneration(RegenerationOption.Manual)]
     public class Class1 : IExternalCommand
     {
          public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
          {
               //Get application and document objects
               UIApplication uiapp = commandData.Application;
               Document doc = uiapp.ActiveUIDocument.Document;

               //Define a reference Object to accept the pick result
               Reference pickedref = null;

               //Pick a group
               Selection sel = uiapp.ActiveUIDocument.Selection;
               pickedref = sel.PickObject(ObjectType.Element, "Please select a group");
               Element elem = doc.GetElement(pickedref);
               Group group = elem as Group;

               //Pick point
               XYZ point = sel.PickPoint("Please pick a point to place group");

               //Place the group
               Transaction trans = new Transaction(doc);
               trans.Start("JoinGeo");
               doc.Create.PlaceGroup(point, group.GroupType);
               trans.Commit();

               return Result.Succeeded;
          }
     }
}

I get this code on a tutorial from autodesk.

[1240904365 · Accepted solution]

The element you select is not a group .

[fdkuenneke]

As far as I am aware, proper Transaction syntax is as follows:

using (Transaction tx = new Transaction(doc))
            {
                tx.Start("Your Transaction Name");
                //Do your stuff!
                tx.Commit();
            }

This is due to the fact that Transactions expect to be disposed (In this case, being disposed by the convenient Idisposible interface as an object). Let me know how this works for you.