featured content error on headlines

[harris414]

I am getting the following error on my site,

Notice: Undefined index: p in /var/www/vhosts/monstermx.com/httpdocs/live/wp-content/themes/streamline_30/functions.php on line 51

Here is the area of line 51 in functions.php

PHP Code:

 if (strlen($_GET['p']) > 0) {
      echo "<p>";
      echo $content;
      echo "&nbsp;<a rel='nofollow' href='";
      the_permalink();
      echo "'>".__('Read More', 'studiopress')." &rarr;</a>";
      echo "</p>"; 


Does anyone see what is wrong