I found a bug in blogSidebar 2.4 component.
When the admin changes the values in the component setting,
those settings are not saved.
Empty values go in to the config file, this makes the side
bar module not find the correct setting so it displays
nothing when users click on the date in the calendar.
A simple fix is to put those lines:

$columns = mosGetParam($_REQUEST, 'columns';
$intro = mosGetParam($_REQUEST, 'intro';
$leading = mosGetParam($_REQUEST, 'leading';
$links = mosGetParam($_REQUEST, 'links';


above the line:

saveConfig ($option, $columns, $intro, $leading, $links);

in /administrator/components/com_blogsidebar/admin.blogsidebar.php