Good evening Dushan and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the error 500 message you have received on your site.
I would love to help you with this topic.
I took a look at your website and the Community Events page displays nicely on my end.
As anything changed on your end ? Can you confirm if you are still experiencing this issue ?
Other than that your license seems to be valid and attached to the correct website.
This might be related to the fact that the Events Calendar is a network plugin while Community Events is not.
If you have not already done so, you might want to read the following: https://theeventscalendar.com/knowledgebase/multisite-license/
Best regards,
Geoff B.