Recently in my job using MacOSx I discovered -with the help of my peers- an error on the system software updates. Googling and making some calls to our Internet Provider found the problem.
The cisco epc3825 router firmware have a bug managing the CRC of big files. In our particular problem the mac software updates need download files with an important size, when the operating system was installing the updates an error about the files integrity ocourred and the updates were impossible to install.
Other problems with the same source are ocurring in different operating systems, here some links aboute the problem:
Finally the trouble was resolved changing the router by our Internet Provider which had the problem documented, free of course.