Warning: fileperms() [function.fileperms]: stat failed

Replacing image give the following error:

Warning: fileperms() [function.fileperms]: stat failed for /ww/wp-plugins/enable-media-replace/upload.php on line 93

Otherwise uploading new images/media in the media section have no permission problem .
What can I do?
I tried the change-uploaded-file-permissions plugin, with no success replacing the images.
https://www.ads-software.com/plugins/change-uploaded-file-permissions/

https://www.ads-software.com/plugins/enable-media-replace/