I think both datareader and executescalar use a database connection, and from what I've read on the web (sample code), the executescalar uses a connection that can subsequently be closed after use. Maybe you could experiment with closing your connection (note, this is not closing a datareader or execute scalar, but the _connection_).

For instance, I see the oConn (in your case) get closed after the oCmd (in your case) gets disposed.

I've learned a few things with shaking up some dot net code, but clearly you still want to test plenty! Obviously just a suggestion, and I could be completely full of it!