setting a 150 character excerpt of the content for meta description

Hello,

Like I said in the title, I would like the put a 150 character excerpt of my content at meta description.

Neither %%excerpt_only%% nor %%excerpt%% works.

What I get is:

<meta name="description" content="%%excerpt_only%%"/>

http://wordpress.org/extend/plugins/wordpress-seo/

Edit: I’m sorry I forgot to delete to page’s meta description page, so it’s now working perfectly. You can delete this thread.