Index: wp-content/themes/twentyten/functions.php
===================================================================
--- wp-content/themes/twentyten/functions.php	(revision 39994)
+++ wp-content/themes/twentyten/functions.php	(working copy)
@@ -536,7 +536,7 @@
 function twentyten_posted_in() {
 	// Retrieves tag list of current post, separated by commas.
 	$tag_list = get_the_tag_list( '', ', ' );
-	if ( $tag_list ) {
+	if ( $tag_list && ! is_wp_error( $tag_list ) ) {
 		$posted_in = __( 'This entry was posted in %1$s and tagged %2$s. Bookmark the <a href="%3$s" title="Permalink to %4$s" rel="bookmark">permalink</a>.', 'twentyten' );
 	} elseif ( is_object_in_taxonomy( get_post_type(), 'category' ) ) {
 		$posted_in = __( 'This entry was posted in %1$s. Bookmark the <a href="%3$s" title="Permalink to %4$s" rel="bookmark">permalink</a>.', 'twentyten' );