Combinate 10.6.8 update could not uncompress

I've got MacOS X 10.6.6 installed in my MacPro and I wanted to update to 10.6.8 but when I download the combinate update and try to install it, it appears this screen that says:

The update "Combinated Update for Mac OS X" cannot be installed.

The update could not uncompress. Maybe the file has been corrupted during download. This update will download again and checked next time Software Update runs.

Does anyone know how to solve it? I've tried to check if the download is available somewhere else, but I haven't been able to find it.

Thank you very much! 🙂