This happend to me when I tried to load ajax-content in internet explorer (worked fine in Firefox, etc), which had a script-tag without a valid comments tag.
So just for the record, here is the solution, which helped me.
Before (Broken):
<script type="text/javascript">
<!--
alert('text');
// -->
</script>
Fixed (Working)
<script type="text/javascript">
// <!--
alert('text');
// -->
</script>
