I have the exact same problem.
What we are doing in this particular exercise out of the book is setting up a datagrid and grabbing tables from the SQL "pubs" database to fill the datagrid. In order to do this, we first create a connection string ("server=(local);database=pubs;uid=sa;pwd=") which should work for connecting to the default local SQL Server 2000 installation, and then we open that connection (which is created as "myConnection"). When it gets to myConnection.open(), it creates the referenced system error. I have tried changing the connection string, thinking that was the problem, and even reinstalled SQL in case I did something stupid the first time I installed it, and I still get this error.