WHERE clause specifying date range causing "Connection must be valid and open" error

[Grommit Wallace]

I've simplified my question from a prior posting. I'm using MySQL 4.1.11 and MySQL Connector NET 1.0.4 on Windows XP SP2.

The following query works when issued via MySQL Query Browser:
"SELECT * FROM Events WHERE Eventdate >= '2005-07-01 08:00:00Z' AND Eventdate <='2005-07-01 09:00:00Z'"

So the query is syntatically and logically correct.

Yet when my code tries to fill a Dataset with the results of the above query using the following code:
string CS = "Database=abc;Data Source=localhost;User Id=grommit;Password=wallace;";
MySqlConnection conn = new MySqlConnection(CS);
conn.Open();
MySqlDataAdapter da = new MySqlDataAdapter(sql, conn); // sql = query above
DataSet ds = new DataSet();
da.Fill(ds); // Exception thrown here...

I get an error on the line "da.Fill(ds)" :
"System.InvalidOperationException:Connection must be valid and open." is thrown when the following query is issued:

The above code works great for other queries. It's when I add "WHERE Eventdate >= '2005-07-01 08:00:00Z' AND Eventdate <='2005-07-01 09:00:00Z'" that the error appears.

What am I doing wrong? Help....

FYI: The table Events used in the query above is defined as:
CREATE TABLE `events` (
`Id` varchar(36) NOT NULL default '',
`EventDate` datetime NOT NULL default '0000-00-00 00:00:00',
`DetailId` varchar(36) NOT NULL default '',
`RecurrenceId` varchar(36) default NULL,
`Active` tinyint(1) default NULL,
....