Are you using the demo version? In that version, you can't save games, so I'd also guess that the rated games feature might not work either.
HELP - Shredder rated games - doesn't seem to work

If you go to the Help menu, and if the "Register..." submenu is greyed out, then I'd guess the program thinks you've registered the program.

Also, if you go to the Help menu, you can click on "Query Program Update..." to see if you have the latest update.
Thanks I've done both - it is registered and appears to be the latest version and it seems to derive my rating if I select the strength when starting a new game, but nothing shows when I go to results it says I have to play a rated game.

Well, I don't know. I pulled up my copy of Shredder 12 and tried playing a rated game, and at first it didn't seem to want to record the result. I fiddled with some settings and eventually logged out and back in, along with a reboot. It finally started working, though. (I never recall ever having this problem before, it's always worked OK.) It's possible that I might not have done something right that time.
You might try logging out/in, or even rebooting to see if the problem goes away.

I'm using shredder classic, but it doesn't seem to rate my games - is there a minimum strenght opponent needed or is it something else. I've checked the rated game box in the options and its also ticked when i start a new game.
To answer your first question, the rating you set shouldn't matter; The problem has to be something else.

Maybe if I stop using the take-back feature ?
I've tried my setup both with and without using the take-back feature, and it doesn't seem to make any difference; It saves my rating information in either case.
I'm beginning to wonder whether there might be a permissions issue with the folder that's supposed to contain the rating information. For my setup, the file containing my rating information is named rating.dat, and it's located in my folder named "C:\Users\(your account name)\AppData\Roaming\ShredderChess\GUI12". (For Shredder Classic 4, I'm guessing that the GUI12 folder would have a different name.) I'm using Windows 7.
You might want to look in that folder to see if the rating.dat file exists, and you might also try to copy a sample file into that folder to see if your OS lets you do it.
If none of this works, I'm guessing you might be at the point of contacting Stefan Meyer-Kahlen at http://www.shredderchess.com/support.html to see if he can help with your problem.

One more question - You're not running Windows 10, are you? Seems I heard that some people are reporting file permission problems with some software in Windows 10.
I'm not running Windows 10 - but I am running Shredder under a normal user account - ie not an admin account.

It seems to be move take-back - you cant take back in rated game
Do you mean that it won't let you take back a move in a rated game at all, or do you mean that if you take back a move in a rated game, then the game doesn't get rated?
Note that when you click on "New game", the new game popup box has an option titled "Strict Rules (No Takebacks)". If you uncheck this option, Shredder should let you take back moves in rated games. (Although if you take back a move and then make a different move, Shredder will ask you if you want to create a new variation, in which case you should answer "No".)

What about the discussion in Post #10? Did you see if the rating.dat file exists, and if you can copy files to the folder containing rating.dat?
It won't let me take back in a rated game.
There wasn't a rating.dat file but there is now.
I have sucessfully played a rated game -thanks for your help and patience.

It won't let me take back in a rated game.
There wasn't a rating.dat file but there is now.
I have sucessfully played a rated game -thanks for your help and patience.
OK, glad I could help, although I'm not sure what I did to help, exactly.
Do you know what was causing the problem?

I had to select rated game and no take-backs in the new game dialogue
OK, thanks for letting me know how you fixed it. It's really odd, though...My GUI rates games even if I allow take-backs in the new game dialogue (and it actually will let me take back moves in a rated game, which isn't really kosher). Maybe there's a slight difference between the Shredder 12 GUI and the Shredder Classic GUI, idk.
I'm using shredder classic, but it doesn't seem to rate my games - is there a minimum strenght opponent needed or is it something else. I've checked the rated game box in the options and its also ticked when i start a new game.