As I've already mentioned this code should not contain line breaks. try these variants:
<div style="overflow: hidden;">
<script>googletag.cmd.push(function() { var mappingInComments = googletag.sizeMapping().addSize([0, 0], [300,250]).addSize([336, 0], [[336,280],[300,250]]).build(); googletag.defineSlot('/283405443/PTP//news//article//in_comments', [300, 250], 'div-gpt-ad-in_comments-1').defineSizeMapping(mappingInComments).addService(googletag.pubads()); googletag.enableServices(); googletag.display('div-gpt-ad-in_comments-1');});</script>
</div>
<div style="overflow: hidden;"><script>googletag.cmd.push(function() { var mappingInComments = googletag.sizeMapping().addSize([0, 0], [300,250]).addSize([336, 0], [[336,280],[300,250]]).build(); googletag.defineSlot('/283405443/PTP//news//article//in_comments', [300, 250], 'div-gpt-ad-in_comments-1').defineSizeMapping(mappingInComments).addService(googletag.pubads()); googletag.enableServices(); googletag.display('div-gpt-ad-in_comments-1');});</script></div>
<script type="text/javascript">
googletag.cmd.push(function() {
var mappingInComments = googletag.sizeMapping().addSize([0, 0], [300,250]).addSize([336, 0], [[336,280],[300,250]]).build();
googletag.defineSlot('/283405443/PTP//news//article//in_comments', [300, 250], 'div-gpt-ad-in_comments-1').defineSizeMapping(mappingInComments).addService(googletag.pubads());
googletag.enableServices();
googletag.display('div-gpt-ad-in_comments-1');
});
</script>