for some users profile pictures are not getting updated in AD

Hi,

  For some users profile pictures are not updating or synchronizing in AD from SharePoint. When I checked for the picture urlin database it is null for all users. Even I used a powershell script using userprofile manager to get the picture url value for all users but it is still giving no result. In MIISClient I checked for those users data is not at all exporting or coming in the log after running incremental sync.

So my questions are

1) what to do next in order to resolve this issue.

2) Why Picture URL is null when every user has picture in mysite.

Please reply asap