my mac cannot connect to the software update center. what is wrong?

Hello papposkonstantinos,

Thanks for visiting Apple Support Communities,

We understand that you are unable to download the latest software update on your Mac. The next best step is to attempt to download the update after entering safe mode. This should help, and the following guide provides instructions on how to do so:

Use safe mode to isolate issues with your Mac

Best regards.

Cheers.

Sometimes the URL of the Apple Software Update Server is replaced with a private one used inside a company, or one in the back room of an Apple Service Center if your Mac has recently been serviced.

If that is the case, moving the file to the desktop named:

com.apple.SofwareUpdate.plist

from the folder

/Library/Preferences

and restarting ...

sometimes sets it back to the default Apple Server.