Copy Page in Sitemap, Error:Failed to load resource: the server responded with a status of 500 (Internal Server Error)

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Hello Community,

we use the concrete5 Version 8.1.0. Copying a page in the sitemap causes the following error:

Error:Failed to load resource: the server responded with a status of 500 (Internal Server Error)

If I debug then I get the error Whoops \ Exception \ ErrorException (E_ERROR) Class 'Concrete \ Core \ Page \ DuplicatePageEvent' not found (Screenshot)

Concrete5 is by default and the core code has not changed. Has anyone else also this problem in the current version or has someone a solution. I am looking forward to your feedback. Best regards Frank

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