Thanks for your answer, Kate.
I’ve re-uploaded the plugin by FTP. The problem persists in at least three different blogs where I’ve installed the plugin. In order to check possible incompatibilities, I’ve deactivated all plugins, except Akismet, but this action doesn’t solve the problem.
My PHP skills are very limited, but I suspect there is something wrong with /admin/settings.php file, in lines 45-56. When commenting these lines, everything looks fine.
The only blog where I’ve got the plugin to work well is the one with the option “Discourage search engines from indexing this site” enabled, which reinforces my suspicion that these lines have something to do with the problem, as version 3.5 contains new code related to this option, in lines 45-56.
On the other hand, please look at the translation functions for lines 50 and 53. When trying to translate them to spanish with Poedit, this program can’t read properly these two lines:
<h3><?php _e('This site is hidden from Search Engine. <a href="'.$visibilityadminpage.'">WordPress block access to Robots</a>','private-only'); ?></h3>
<h3><?php _e('This site is visible to search engines, go to the <a href="'.$visibilityadminpage.'">reading settings</a> page and select the "Discourage search engines from indexing this site" box to hide this site.','private-only'); ?></h3>
When I update PoEdit to create the .PO file, the program reads the two strings incompletely, as follows:
This site is hidden from Search Engine. <a href=\"
This site is visible to search engines, go to the <a href=\"
So, I think they are not well prepared to be translated.
As I’ve said before, my PHP knowledge is very poor, but can these two problems be related?