Strange wordpress .htaccess file problem.

Here I am again asking for help, i`m sure soon i`ll be helping noobs like me.

The last couple of days my site has gone down with 500 error, so checked out the .htaccess file and noticed a lowercase s right at the bottom of the code.

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress
s

Click to expand...

Notice the lowercase s, so i deleted the s and all was good but it just keeps happening.

I do have amazon poster plugin but the times of this happening don`t match up.