Update: Blogger has Rolled back the Light Box Feature. So there is no point in reading further.
Go to Template > Edit HTML and paste the following Code Snippet above </body>
<script type='text/javascript'> document.getElementById('Blog1').id = 'Blog222'; var bp_dummy = document.createElement("div"); bp_dummy.id = 'Blog1'; bp_dummy.style.display='none'; document.getElementsByTagName("body")[0].appendChild( bp_dummy ); </script>
In this Code, Blog1 is the id of your Blog Posts Widget.
Save The Template, and LightBox wont be bothering you anymore :) I use the same technique here on my Blog :)