That is a problem where proevents has not been updated to be compatible with latest php and mysql.
The class 'Object' can no longer be used, so the core changed the class declaration to class ConcreteObject.

Modifying the proevents code to use ConcreteObject may help. However, proevents is not maintained and has not been updated in many years, so you will undoubtedly run into further issues.

Hi JohntheFish,

thx for the info.
Is there a way to easily uninstall ProEvents manually?

Options (backup the database first):

a) I you can get to the extend page in the dashboard, click to uninstall there and hope for the best!

b) Revert your database to a state before proevents was installed

c) fix proevents well enough to be able to uninstall it as per (a) (you won't need a full fix, just some critical code)

d) Hack the database to remove the proevents installation from all blok/package/attribute
tables. This is manageable for simple block packages, but likely to be too complicated to be achievable for pro-events.

e) Revert your server software 'till proevents works, unistall, then get server current again.

f) clone site onto an older server, uninstall proevent, then clone back to your live server

ohhh.... since I am not such a techie, I will leave it as it is :)
option a) dit not work always showing error as shown in attachment