WYSIWYG does not load wp-tinymce 500 internal server error

hi all,

i have a very irritating problem with my wysiwyg editor.
It just does not show up. it shows the buttons you get when pressing the HTML tab.
when u press the HTML tab you see nothing change. when clicking on WYSIWYG again the button bar disappears and still see the html of the post.

i checked everything. upgraded to latest version (3) and removed all plugins.

it seems that the wp-tinymce.php gives a 500 internal server error. But the strange thing is that the file exists. and i don’t see any errors.
i also tried replacing it with the wp-tinymce of a older version.
all not helping out

/wp-includes/js/tinymce/wp-tinymce.php?c=1&ver=327-1235