Replace your code with this:
Options +FollowSymLinks -MultiViews
# Turn mod_rewrite on
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^/.]+)/?$ index.php?a=profile&u=$1 [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(([^/]*)+)(/([^/]{0,32})(/.+)?)?$ index.php?a=$1&q=$3 [L,QSA]