[Plugin: NextGEN Gallery]Thumb generation problem

Hi, and thx in advance for help !

I’ve a problem with Nextgen to create thumb :

If i try to generate Thumb, i’ve this error : can’t access wp-admin/admin-ajax.php.
If i change permission in 777 for this file, i’ve this error : Internal Server Error.

In fact, pictures are upload on my website and i’ve always the tirht/fourth thumbs create and not others…

My php.ini is config on my dedicate for test :

– post_max_size = 1000M
– upload_max_filesize = 1000M
– max_execution_time = 900
– memory_limit = 256M

and i don’t have this problem with my other website on my dedicate…

Can u help me ?