How about :
Database db = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Database;
using (Transaction tr = db.TransactionManager.StartTransaction()) {
BlockTable BlockTable = tr.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
ObjectId modelSpaceId = BlockTable["*MODEL_SPACE"];
BlockTableRecord modelSpace = tr.GetObject(modelSpaceId, OpenMode.ForRead) as BlockTableRecord;
BlockTableRecordEnumerator iter = modelSpace.GetEnumerator();
ObjectId lastObjId = new ObjectId();
while (iter.MoveNext()) {
lastObjId = iter.Current;
}
DBObject lastObject = tr.GetObject(lastObjId, OpenMode.ForRead);
tr.Commit();
}
HTH
Jai
