Error message on activation

Hm – I can’t replicate this. Are you able to look in your error logs for any kind of additional information?

I got the same error so uninstalled.

I saw the same issue. Also when I go to the media page in admin I get this where the file size should be:
Warning: filesize(): stat failed for /path/to/image.jpg in /path/to/site/wp-content/plugins/media-file-sizes/media_file_sizes.php on line 141

This is only with debug = true.

I found that this happens only with images that do not exist and/or are missing (imported database without downloading uploads directory).

This fixed it. Added the following to line 141 before the filesize() call:
if ( ! file_exists( $orig_full_path ) ) return;

Cool, thanks for this. I’ll try to get it incorporated soon.