In your CUtags.php, the dates are shown in Spanish. You need to change in Settings.php $SITE['monthNames'] = array( // for wxastronomy page .. replace with month names in your language
'January','February','March','April','May','June',
'July','August','September','October','November','December'
);
to $SITE['monthNames'] = array( // for wxastronomy page .. replace with month names in your language
"enero","febrero","marzo","abril","mayo","junio",
"julio","agosto","septiembre","octubre","noviembre","diciembre"
);
so the dates can be handled correctly (by translating Spanish months to English for PHP calculations, then back to Spanish if needed).