need help in meta description

Hi Freinds, need all your valueble help. i am using Blogger site. last week when i checked google webmaster tool it was reported 12 of url are having duplicate meta description. i checked my site and found it true. but i find it so hard to replace the duplicate meta description.
can anybody tell how is it possible to correct it (i am using blogger)

 

maybe its because you use

<b:if cond=’data:post.url == “http://yourblog.blogspot.com/2007/12/your-post-url-here.html”‘>
<meta name=”description” content=”Your Meta Description Content Here.”/>
</b:if>

Code (markup):

but you're not adding

<b:if cond=’data:post.url == “http://yourblog.blogspot.com/2007/12/the-new-post-url-goes-here.html”‘>
<meta name=”description” content=”Your Meta Description Content for your new post goes Here.”/>
</b:if>

Code (markup):

so each url you'll get same meta description

if you still confused, i have reference site for that