Error - Object reference not set to an instance of an object.

[FredC]

OS Name Microsoft Windows XP Professional
Version 5.1.2600 Service Pack 2 Build 2600
Total Physical Memory 1,024.00 MB

MDE 2003 Version 7.1.3008
..NET Framework 1.1 Version 1.1.4322 SP1
Microsoft Visual C# .NET 69462-335-0000007-18707
Crystal Reports for Visual Studio .NET AAP50-GS0000S-WCK00C3

I use an event handler as follows:

private ArrayList WTGData_10 = new ArrayList();
private void WTGDataRowReady 10Handler( WTGDataGroup_10 myWTGData )
{
WTGData_10Timer .Enabled = false;
try
{
WTGData_10.Add( myWTGData);
}
catch( Exception ex)
{
WriteToEventLog s.logWrite("WTG DataRowReady10H andler: " +
ex.Message, Utility.Trilliu mConstants.WTGL og);
}
WTGData_10Timer .Interval = 9999;
WTGData_10Timer .Enabled = true;
}

There may by 50 + calls to the handler on a ten minute event timer. The
handler stuffs the struct (WTGDataGroup_1 0 myWTGData) into the collection
myWTGData.

Once the timer WTGData_10Timer times out the following timer event handler
(onCalcTimedEve nt) trys to send the data to a SQL Database. The error occurs
in the following code while trying to equate myWTGData =
(WTGDataGroup_1 0)WTGData_10[i].

Note: The firct call to onCalcTimedEven t works fine - the records are
successfully written to the SQL database. All subsequent calls result in the
Object reference error.

public void onCalcTimedEven t(object source, ElapsedEventArg s e)
{
// local struct storage
WTGDataGroup_10 myWTGData = new WTGDataGroup_10 ();

// WTGData_10 is the collection that has been filled by the event handler
// Add each row from the collection WTGData_10 to the data set

// get a copy of the first row
myWTGData = (Trillium.WindS pace.WindSpace. WTGDataGroup_10 ) WTGData_10 [0];
// add it to the empty DS10MinData
DS10MinData.Cle ar();
addData(myWTGDa ta);

// add the rest, checking that there are no dups
for(int i = 1; i < WTGData_10.Coun t; i++)
{
bool bDupFlag = false;
try
{
//*********Error occurs here*********** ********
myWTGData = (WTGDataGroup_1 0)WTGData_10[i];
foreach ( DataRow DR in DS10MinData.Tab les "Turbine10Minut eData"].Rows)
{
// test if myWTGData row equals anything already in the Dataset DS10MinData
if ( (myWTGData.Turb ineID == Convert.ToInt32 (DR["Turbine ID"]))
&& (myWTGData.Turb ineCircuitID == Convert.ToInt32 (DR["Circuit ID"])) &&
(myWTGData.dt == Convert.ToDateT ime(DR["Date"])) )
{
//yes this myWTGData has a duplicate in the data set - don't add it
bDupFlag = true;
break;
}
}
}
catch( Exception ex)
{
//*************** ***ERROR handled here *****
WriteToEventLog s.logWrite("onC alcTimedEvent: testing for dups error: " +
ex.Message, Utility.Trilliu mConstants.WTGL og);
}
// if this is not a duplicate add it to the Data set
if ( !bDupFlag ) addData(myWTGDa ta);
bDupFlag = false;
// go on to the next element in the collection WTGData_10
}

// send the dataset to the data base
try
{
#region "SQL stuff"
// code not shown
#endregion
adpTurbine10Min Data.Update(DS1 0MinData);
adpTurbine10Min Data.Dispose();
}
catch( SqlException ex)
{
WriteToEventLog s.WTGLogWrite(
"WTGCube-onCalcTimedEven tonCalcTimedEve nt-Can't write to to TrilliumWind Db,
SQL Exception -" + ex.Message);
}

// remove all elements for the DS and the collection
DS10MinData.Cle ar();
WTGData_10.Clea r();
}