Error appears in checkout, blocking it

Hello!
Sometimes an error appears in the page of checkout on my website… I do not remember exactly the error, but in the link there is the path to your plugin, something like: Error….https://mywebsite.com…/…./cm-dual-registration…

This error stops the procedure of checkout so I really need to fix it…
Can you help me or the details given are too poor? ??

Thanks
Francesca

https://www.ads-software.com/plugins/campaign-monitor-dual-registration/