I see lots of people having problems with this - I did too - but what some of you are doing isn't working.
What seems logical is to cut'n'paste someone's name (because who wants to type it out when it's long and complicated, right? ) then putting an '@' in front of it and you think it'd be all sorted.
Trouble is: it doesn't work. The clue is when you send your post and the @ has notPalacono.
Unfortunately you do have to type the name in (there are other ways, but it's more complicated) starting with the @ then the rest of the name. and it'll all change colour, like this: @Palacono.
Frustrating, and prone to error, because if you misspell someone's name, it'll still change colour, like this @PalaPalaconocono even if that person does not actually exist.
So, if you've 'tagged' someone in a post and they've not replied; that's probably the reason.
(And the staff members just taking over from @SimonKJones: you're doing this too. )
Best of luck.