bit confused with ne...pas Le passe compose/ present indicatif for depuis longtemps.

You have used the present tense with depuis longtemps which is correct for "not long". The problem is the use of «n'arrive pas» - this doesn't translate to "I haven't been . . .     ' which is  «Je ne suis pas en France depuis longtemps».

You arrived in the past, so it has to be the passé composé, not the present. But I know that does seem to contradict the rules given in the lesson. This question gets asked a lot, I'm still not sure I understand it, but I'll repeat what I wrote last time about a similar example:

According to the lesson, the present tense is translated as "not long", but the passé composé should be translated as "not in a long time". So it should mean "Martin hasn't arrived in a long time", but it seems to be following the rule for the present tense instead. 

When arriver means "to happen", I think you do get the expected meaning according to the rules:

"ça n'est pas arrivé depuis longtemps" = "that hasn't happened in a long time"

If I had to guess at an explanation for this, I'd say that the rules in the lesson should be considered just as rules of thumb. When you have a negative sentence it could either be negating the verb (= it didn't happen) or the "longtemps" (= not long). You have to work out which it is from the context.

Hi Cécile, 

It looks a little odd to me, too, but one of the examples in the lesson is this:

Martin n'est pas arrivé depuis longtemps = Martin hasn't been here long.

I think there is also a similar quiz question as Anish says.