Since the author of this extension himself describes it as "obsolete" and discontinued the development, it is not compatible with TYPO3 as of version 4.6 anymore. You should avoid to install "mininews" where possible and maybe shift running installations - especially if you cannot preclude an upgrade to newer TYPO3 versions in the future.
As an alternative, we recommend using tt_news, which is under active development, compatible with all new TYPO3 versions and has a great range of functions.
In addition, the TYPO3 extension "news" is an interesting alternative. It offers a similar range of functions like tt_news, and is technically more modern. More detailed information can be found in the TYPO3 Extension Repository.
Nevertheless, our short description of the mininews extension is still available for your information: