Frank Ralf wrote:
shall I copy
the include directory from the old to the new wiki???
Yes
Uh? You should only use the include directory coming with your version.
It is the contents of the *extension* directory what you may copy
(although better to check if there's a newer version available).
Also, that error is often produced by having
require_once("extensions/Foo/Foo.php"); instead of
require_once("$IP/extensions/Foo/Foo.php");