What is the best way of handling a uniquieidentifer that has been stored in a session state, and then trying to get it back and save it.

I am trying to execute the following but getting an error because the session is in a string format. I don't see a way to convert it to a unique identifier.
using (SqlConnection objConnection = new SqlConnection(strConnection)) { using (SqlCommand objCommand = new SqlCommand("MyInsertCommand", objConnection)) { objCommand.CommandType = CommandType.StoredProcedure; objConnection.Open(); objCommand.Parameters.Add("@UserID", SqlDbType.UniqueIdentifier).Value = (string)(Session["LoginID"].ToString()); objCommand.Parameters.Add("@Identity", SqlDbType.Int, 0).Direction = ParameterDirection.Output; // Having the variable @Identity set in the SQL insert command, we can get it back in the next sequence objCommand.ExecuteNonQuery(); ...