I am running two blogs on one site. Blog #2 is in a subdirectory, Blog #1 is the main site. The built-in site search works fine on Blog #2 (in the subdir), but does not return any results on Blog #1, not even using known good search terms.
Here is the search code for Blog #1:
<div class="searchbar">
<form method="get" id="searchform" action="http://www.meria.net">
<input type="text" value="" name="s" id="s" onfocus="this.select();" />
<input type="submit" id="searchsubmit" value="Search" />
</form>
</div><!--/searchbar-->
Here is the search code for Blog#2:
<div class="searchbar">
<form method="get" id="searchform" action="http://meria.net/meria/">
<input type="text" value="" name="s" id="s" onfocus="this.select();" />
<input type="submit" id="searchsubmit" value="Search" />
</form>
</div><!--/searchbar-->