I am using php to generate an array of photo thumbnails that are clicked through in order. I am also using a popup window to display the full image. The images swap from one to the next with no problem until they are clicked on and the popup function is called. After closing the popup window and clicking to the next image, the new image is not displayed (in IE only, Netscape 7 is fine) - you have to right-click and do Show Picture to see the image again. Does anyone have any idea why this is happening? My code for my swap and popup functions are as follows:

var photo_counter = 0;

function swap(dir, photos) {
if (dir == 'left') {
photo_counter--;
if ( photo_counter < 0 ) {
photo_counter = photos-1;
}
document.getElementById('photo_text').innerHTML = 'Photo ' + eval(photo_counter + 1) + ' of ' + photos;
document.getElementById('photo_caption').innerHTML = arr_desc[photo_counter];
void(document.getElementById('photo').src = arr_photos[photo_counter]);
}
else {
photo_counter++;
if ( photo_counter >= photos ) {
photo_counter = 0;
}
document.getElementById('photo_text').innerHTML = 'Photo ' + eval(photo_counter + 1) + ' of ' + photos;
document.getElementById('photo_caption').innerHTML = arr_desc[photo_counter];
void(document.getElementById('photo').src = arr_photos[photo_counter]);
}
}
function pop_up(){
var features_str = "width=" + arr_widths[photo_counter] + ",height=" + (arr_heights[photo_counter] + 20);
var url = 'view_photo.php?photo=' + arr_photos[photo_counter] + '&width=' + arr_widths[photo_counter] + '&height=' + arr_heights[photo_counter];
window.open(url,"viewer",features_str);
return;
}

I have tried everything I can think of, but to no use. Help!!!
Thanks.