I accidentally included 2 files in the zipfile. Sorry, my mistake. There's just one now: news_manager.php, which should be placed in your plugins folder.
@El-Cherubin: removing the previous files and replacing them with the new news_manager.php probably solves your problem.
@Oleg06: I think you're getting those messages because you probably have DEBUG mode turned on. If so, it's safe to ignore them. About your second question, I don't really get it. Clicking on the title of an article in the admin section should bring up the edit screen.
@El-Cherubin: removing the previous files and replacing them with the new news_manager.php probably solves your problem.
@Oleg06: I think you're getting those messages because you probably have DEBUG mode turned on. If so, it's safe to ignore them. About your second question, I don't really get it. Clicking on the title of an article in the admin section should bring up the edit screen.