Always make sure the class file is exactly named FooPage.class.php (replace Foo with a name of your choice) and the class itself must be named "FooPage" (again appending the "Page" component).
the correct file name would be LinkPartnerManagementPage.class.php and the class name should be LinkPartnerManagementPage. WCF wants the first letter of a class (and its file name) to be uppercase.