Sometimes the cause of such issues is sharethis plugin incompatibility with the theme of the wordpress blog.
In that case , you will have to add the buttons manually to your blog.
Here are the detailed steps:
Sharethis script and span tags go on the page where you want the buttons to appear and they also determine what kind of button appears as well as what URL and title it shares. You will have to put 'script tags' in your Main index template(index.php) and 'span tags' in Single Post template(single.php).
Here is the basic span for just the ShareThis button: <span class="st_sharethis" st_title='<?php the_title(); ?>' st_url='<?php the_permalink(); ?>' displayText="ShareThis"></span>
You can change the class of the span to determine the button that appears. For example class="st_twitter" will make a twitter icon and class="st_email_vcount" will make a email vertical counter button.
However, adding code in index.php and single.php will not display sharethis buttons on the blog page but will show buttons whenever an individual post is opened.
If you wish to display sharethis buttons on the blog page ,you will have to put 'span tags' in (loop.php).
1. put span tags just above the line "<div class="entry-utility">" to display buttons at the end of each post on the blog page.
<span class='st_sharethis' ></span>
2. to display buttons at the beginning of each post on the blog page,put span tags just below the lines
<h2 class="entry-title">" title="<?php printf( esc_attr__( 'Permalink to %s', 'twentyten' ), the_title_attribute( 'echo=0' ) ); ?>" rel="bookmark"><?php the_title(); ?></h2>
<?php twentyten_posted_on(); ?>
</div><!-- .entry-meta -->
<?php if ( is_archive() || is_search() ) : // Only display excerpts for archives and search. ?>
Hope this helps.
[ sharethissupport, all of your posts are being held in moderation and will need to be approved before users can see them. Please follow the rules and refrain using signatures in your reply posts. ]