Okay, I overlooked this small but fine detail. Thank you.
Meanwhile I have found out that the error message appears if I insert the topical phpbb_seo\includes\setup_phpbb_seo
(During the update from Ultimate Seo Mod from 0.6.2 to 0.6.4).
The topical file is much bigger like the previous file.
Is it necessary to replace the file or not?