thumbnails with default style don't show

I can also confirm this. The problem appears to be only with the default main slider. If you use the Nivo Slider Formatter the thumnails options works ok.

I think there is something wrong when setting the parameter from the admin, but I will have to check.

Thank you for Nivo Slider.

Thumbnails were broken by a previous commit.

The attached patch fixes thumbnail navigation support.

Committed to 7.x-1.x.

After downloading the latest git checkout/development release and enabling thumbnail navigation on the settings page, you should be able to inspect the markup of a page which has the slider and see something like:

<div class="nivo-controlNav">
  <a class="nivo-control" rel="0">
    <img src="http://nivo.dev7studios.com/wp-content/uploads/2011/08/nemo10-70x50.png" alt="">
  </a>
  <a class="nivo-control" rel="1">
    <img src="http://nivo.dev7studios.com/wp-content/uploads/2011/08/slider48-70x50.png" alt="">
  </a>
  <a class="nivo-control active" rel="2">
    <img src="http://nivo.dev7studios.com/wp-content/uploads/2011/08/walle47-70x50.png" alt="">
  </a>
</div>

Unfortunately, none of the default themes included with the nivo slider jQuery plugin support thumbnails out of the box (by default the thumbnail images are hidden). You either need to write your own theme (see the nivo_slider.api.php included with the Nivo Slider module) or modify the CSS of one of the included themes.

To get thumbnails to display with one of the default themes, you'll have to unhide the images and position them.

#slider .nivo-controlNav {
	position:absolute;
	bottom:-70px; /* Put the nav below the slider */
}
#slider .nivo-controlNav img {
	display:inline; /* Unhide the thumbnails */
	position:relative;
	margin-right:10px;
}

See Using Thumbnails with the Nivo Slider for more information.