Error http 500 after login


I just installed Nextcloud and when I try to login with my user, I keep getting the error 500.
In the Apache-log there ist this error message:

[error] [client ***] PHP Fatal error: Declaration of OC\\Files\\Storage\\Local::copyFromStorage(OCP\\Files\\Storage $sourceStorage, $sourceInternalPath, $targetInternalPath) must be compatible with OC\\Files\\Storage\\Common::copyFromStorage(OCP\\Files\\Storage $sourceStorage, $sourceInternalPath, $targetInternalPath, $preserveMtime = false) in /home/www/*****/lib/private/Files/Storage/Local.php on line 43

Can anybody tell me, what this means?

Thanks and regards, mtm