Can anyone explain Facebook notifications to me?

Dear Anyone.
I get E_mails about Fb groups that would be of use to me, or that I should be interested in, but when I click on the enclosed links, the Facebook page always says 'Sorry, unavailable' or 'Sorry, the creator's only made the content available to a small number of people right now' or words to that effect.

As I'm being sent the notifications, shouldn't I be one of the people able to see the content? And why are so many pages I'm being sent E_mails about coming up 'Can't be found', with a picture of a little blue guy with a large spanner in his hand on them?

Don't understand what's going on! All help will be tried.

Yours r espectfully

Chris.