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 TYPO3 version 6 or above one day.
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.
Besides there is another pretty new alternative with similar capabilities, simply called "news". You can get further information about that at the TYPO3 Extension Repository.
Alternative news extension: "tt_news"