help please!

[chiccaita]

Is there anyone who likes to help me?I'va got a problem with the use of duration form. Is it possible to use it in negative forms or not? in many English grammars for italian students they say it's impossible, but there are, in my opinion,situations where you can use it. For example I can say: I've not been walking for a long time, but I am tired
On the contrary you say: I've not visited my uncle since 2002.
Are both examples correct? What's the difference and can I use the duration Form in a negative statement?
Thanks in advance
Enrica

[ziadmasry]

the first sentence is correct because u express a period. and the second sentence is also correct as u express the stop of an action since an exact time.
In my opinion u can use duration in negative forms according to the meaning of each sentence.