Error opening datareader using singleton pattern

Hi, i am developing a web portal in asp.net 2.0 and i am using tableadapters to query the database.
Im getting sometimes the following error: there is a datareader open associated to this command.
The web is beta testing now, but im afraid this error will be more frequent when it will be online.
I use the singleton pattern to access the tableadapter in the bussines access layer and i think the problem is here.
This is the code:
 
 private static agendaTableAdapters.artistasTableAdapter _Adapter = null;

        public static agendaTableAdapters.artistasTableAdapter Adapter
        {
            get
            {
                if (_Adapter == null)
 & ...