[nextgen gallery] – thumbnails not created

Hello,

i tread thousands of posts about my problem but can not solve it.

My hoster has newest php version, safe mode is off, GD Library is active, folder permissions are 755…

but thumbnails are not created. When i put shortcode [nggallery id=3] to my post it shows empty picture thumbnails, when choosing one, the correct picture is shown.
In Gallery Adminsitration (where gallerys are listed), if founnd my three albums, but there is now thumg when choosing one. When clicking on show it shows the correct picture.

When trying to create new thumbs, page is loading a short time, but there is no progress window. the browser just refreshs and nothing more happens.