Problem uploading pictures



I've just installed elgg, and I'm trying to upload pictures.

My hosting is a dedicated server, and the GD libraries are properly installed.

I can upload pfd's, gifs, or some tipe of jpg -I don't know what's the correct type-. The only I can say, is that when the picture comes from a digital camera or mobile phone, I get problems.

The problems are just a blank page after the upload process. If I go back I see a blank icon, and the picture is uploaded but no icon created. 

With photoshop I've converted the same picture to gif, and worked perfectly. Again tryed with jpg, and blank page.

As I say, some jpg pictures taken from websites for example, are ok. But some others drive me crazy.

Anyone can say anything? :-)

Thank you in advance!