[Plugin: WP Users Exporter] Error retrieving …wpue-config

Hello,

First of all: thx for the plugin, would be really convenient for a lot of WP-sites!
& works like a charm (PHP 5.3.3), only when I try to update the options (at options-general.php?page=wpue-config), I get this error message:

The website encountered an error while retrieving https://…/wp-admin/options-general.php?page=wpue-config. It may be down for maintenance or configured incorrectly.

I can retrieve the options, but can’t update them. Any idea?

Kind regards,
Veerle

https://www.ads-software.com/extend/plugins/wp-users-exporter/