Chmod error /Headers already sent error

I’m getting the following error when using the “Replace the file, use new file name and update all links” option.

Warning: chmod() [function.chmod]: No such file or directory in [...]/plugins/enable-media-replace/upload.php on line 125

Warning: Cannot modify header information - headers already sent by (output started at [...]/plugins/enable-media-replace/upload.php:125) in [...]/wp-includes/pluggable.php on line 1173

It doesn’t seem to happen every time – as of yet I haven’t spotted a pattern, sometimes it works fine, sometimes not. I do have a localhost testing site so I can test various scenerios or dump a log file or something if you can’t reproduce and would like me to try something to whittle down the options etc

Note – The file/picture does seem to be replace fine in spite of the error message – aside from breaking the page it appears on, the error doesn’t seem to effect the site.

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