SetInterval Working In Firefox But Not In Internet Explorer

I am entering the so far very exciting world of javascript. However, I am perplexed at the following. I am setting a function to run every second with 'setInterval("runMonitor()", 1000)'. This works magically in Firefox, however works exactly one time in IE6 and then stops.

Code:
function runMonitor(){
var rflag = <?php echo $jsonopt; ?>;
if (rflag == "1"){
return 0;
}

updateSystemUptime();
updateInstanceStatus();
/* updateSystemStatus(); */
} setInterval("runMonitor()", 1000);