help needed please!: Profile picture not showing in ver 1.6 for some users

Hi I'm hoping someone can help me with a problem.

I have a few users who have encountered a problem uploading their profile pic. The upload appears to function ok (I checked the pictures uploaded via ftp) but elgg does not display the pic, only the default shadow picture.

This does not happen for all users and occurs for all image formats . It just affects a few users

Can anyone help?

thanks in advance

Dave