Why is my Process redirect stdoutput is returning different number

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I Have the following in my own library project and I call it from my C#
application twice each time to get Unix group account information and user
account information. But it would return different number of records (lines
of data read), sometimes 0 records without any of my message, and there
doesn't seem to be a pattern to be found. Can someone have a look and see if
any of my code could possbly cause this? Thanks.

static System.Text.Str ingBuilder sb = new System.Text.Str ingBuilder();
static void proc_OutputData Received(object sender,
DataReceivedEve ntArgs e)
{
if(sb.Length 0)
sb.Append("\n") ;

sb.Append(e.Dat a);
}

public static int GetNisFile(stri ng parm, ref DataTable dtAccounts,
ref ToolStripStatus Label slMain, ref StatusStrip ssMain, string
userOrGroup)
{
string accountFile = "", error="";
int numOfAccounts = 0;
System.Diagnost ics.Process listFiles = new Process();
sb.Remove(0, sb.Length);

try
{
listFiles.Outpu tDataReceived += new
DataReceivedEve ntHandler(proc_ OutputDataRecei ved);
listFiles.Start Info = new
ProcessStartInf o(Application.S tartupPath +
"\\ypcat.ex e", parm);
listFiles.Start Info.WindowStyl e = ProcessWindowSt yle.Hidden;
listFiles.Start Info.UseShellEx ecute = false;
listFiles.Start Info.RedirectSt andardOutput = true;
listFiles.Start Info.RedirectSt andardError = true;
listFiles.Start Info.CreateNoWi ndow = true;

if (listFiles.Star t())
{
listFiles.Begin OutputReadLine( );
listFiles.WaitF orExit(30000);
if (listFiles.HasE xited)
{
error = listFiles.Stand ardError.ReadTo End();
if (error == "")
{
accountFile = sb.ToString();
if (accountFile != null && accountFile != "")
numOfAccounts =
CPAUnix.ParseAn dInsertAccounts (accountFile,
ref dtAccounts, ref slMain, ref ssMain,
userOrGroup);
}
else
MessageBox.Show (error, "PowerADvantage ");
}
else
MessageBox.Show ("Time out retrieving NIS " +
userOrGroup + " accounts.",
"PowerADvantage ");
}
else
MessageBox.Show ("Error starting process to read file.",
"PowerADvantage ");
if (listFiles != null)
{
listFiles.Cance lOutputRead();
listFiles.Close ();
}

return numOfAccounts;

}
catch (Win32Exception wex)
{
MessageBox.Show (wex.Message, "PowerADvantage ");
return numOfAccounts;
}
}
--
Thanks.