If you get this error when you try to view your calendar in your browser:

It may be that there is some corruption in the installation.  Here are the instructions to re-install the plugin while saving your events:

– Perform a complete back up of your database before proceeding further
– Delete the file uninstall.php from the plugin directory that is currently on the server (found under /wp-content/plugins/all-in-one-event-calendar). Deleting this file ensures that when you uninstall the current version of the plugin, your event data and calendar settings will be preserved when you delete the plugin (don’t skip this step – it’s important!)
– Deactivate the All-in-One Event Calendar using your WordPress Dashboard.
– Delete the All-in-One Event Calendar using your WordPress Dashboard.
– Database -> wp_options, click option_name to sort and delete everything with ai1ec_, this will delete plugin settings but events will remain in the database.
– Now install the latest version.

If the 500 Server Error appears when you try to download your calendar’s ICS file:

Solution 1:

If you have the 3rd party plugin called “Slider WD” installed, it is known to cause this error.  Simply disable or delete it.

Solution 2:

Some customers reported the error while using PHP version 7.1 (but 7.0 seems to work).

Edit the file: 

plugins/all-in-one-event-calendar/lib/iCal/iCalcreator-2.20/iCalcreator.class.php

and comment out the followig lines (8003-8006):

if( $startdatets <= $wdatets ) { // only output within period
$result[$wdatets] = TRUE;
// echo “recur “.date(‘Y-m-d H:i:s’,$wdatets).”<br>\n”;//test
}