Description:
------------
I am trying to connect to a MSSQL database. Often the first few times this failes giving an error on the server;
"The instruction at "0x0068d6ff" referenced
memory at 0xffffffff. The memory could not be "read"."

The memory adresses always change. I've tried different PHP versions, different Apache versions and different computers but the problem always comes back. It seems to be connected to the ammount of code/size of the query. The more code or the larger the query the more errors I get.

Sometimes it works after a couple of refreshes but the problem always comes back.

Reproduce code:
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<?php

include '..\dbcon.php'; // connect to database

$todays_date = date("Y-m-d"); 
$todays_date = $todays_date.' '; 
$today = strtotime($todays_date);

$query = " SELECT * FROM AddonScheduleCheck ORDER BY starttijd";

$result = mssql_query($query);
$numRows = mssql_num_rows($result);
echo "<table>\n"
	. "<TR HEIGHT='20'></TR>\n"
	. "<TR class='toprow'><TD>\n"
	. "<H2>" . $numRows . " verkeerd" . ($numRows == 1 ? "" : "e") . " roosteritem" . ($numRows == 1 ? "" : "s") . " gevonden " . "</H2>\n"
	. "</TD></TR>\n"
	. "<TR HEIGHT='20'></TR></table>\n";

echo 
	"<table border=4>".
	"<TR class='sub'>\n".
	"<TD width = 120><B>Cursus<BR>Zoeknaam</B></TD>\n".
	"<TD width = 400><B>Cursus Omschrijving</B></TD>\n".
	"<TD width = 500><B>Foutmelding</B></TD>\n".
	"<TD width = 70></TD>\n".
	"</TR>\n";

while($row = mssql_fetch_array($result))
{
	$roostererror=NULL;
	$startdatum = strtotime($row["Startdatum"]);
	$Hoofddocent = $row["HoofdDocentVnaam"].' '.$row["HoofdDocentAnaam"];
	$cursusid = $row["CursusID"];

include 'schedule_error_descriptions.php';

// tekst ipv bits laten zien
	IF ($row["MoederCursus"] == NULL) {$moedercursus='Ja';}
	ELSE $moedercursus='Nee';

 	IF ($row["DatumAnnulering"] == NULL) {$geannuleerd='Nee';}
	ELSE $geannuleerd='Ja';

echo 
	"<TR class='data'>\n".
	"<TD>". $row["Zoeknaam"] . "</TD>\n".
	"<TD>". $row["CursusOmschrijving"] . "</TD>\n".
	"<TD>".	$roostererror . "</TD>\n".
	"<TD ALIGN=center>".	
		"<BR><FORM NAME=\"roostercontrole\" ACTION=schedule_error_details.php?id=$cursusid METHOD=post>" . 
			'<input type="submit" value="Details">' . 
		'</FORM>' . 
	"</TD>\n".
	"</TR>\n";
	
}

//echo "</table>\n\n";

?>

Expected result:
----------------
a table with the rows from the database and a detail button on the end.

Actual result:
--------------
error on the server;
"The instruction at "0x0068d6ff" referenced
memory at 0xffffffff. The memory could not be "read"."