Valid apple id, but not iCloud account

Hi,

I was using iCloud in my MacBook Pro, iPad and iPhone without any problem.

One day, my MBP says 'This apple ID is valid, but not an iCloud account', and I can't log in.

It's only in MBP.. iPad and iPhone works just fine.

I thought some SW configuration problem, so I went back to some weeks agao when iCloud worked fine using Time Machine.

But it didn't work.

I installed again Mavericks... same..

I read some articles about Ethernet port, Mac Address... assuming HW problem.. but Ethernet works very well.

I cheked iTunes and tried to 'authorize this computer', said 'already authorized'.

AppStore.. no problem.

When I tried to create an iCloud account, it says

'This device cannot be used to sign in for an iCloud account.

Sign up using an iPhone 4, iPad or iPod Touch (4th G.)'

Ridiculous... This is MacBook...

I deleted all the login informations in Key Chain... Same....

.... ooooooo

What shall I do more now?

Please, help and save me from this unending digging...