The HTTP server returned following error: Forbidden Error

Hello, i have some weird situtation happening to me,

Here the current issue, 

I have a Powerbi published with 5 tab, 4 are regular matrix / table  and  1 is a graphic with data,

My user can "..." export the 4 rgular matrix/table without an issue, but when they are "..." downloading the graphic chart and opening it on excel after accepting the security pop ups,  they got  

a window with a log in from windows azure and when they put their credential they got >



its only happend to some user, which is weird, because all my users for the dataset and for the reporting have the full "option" read/building/modify for the reporting and for the dataset,

I dont remember having to give access or do something on windows azure but maybe im wrong ?

the error occur only on tab with  dynamc graphic / pie / chart, but it work correctly for any export of table / matrix or flat data 

any help would be hihgly appreaciated