Smush Pro not able to reach server images

This site is unable to reach smush Pro - i've recently experienced this with another site. and we discovered (thanks to support U.Kumar) that the issue was based around sites having a www. redirect. This was fixed on another site by changing wp>setting>general site URL and redirect URL to whatever it wasn't i.e. to make sure it had a www in front of the URL.
Not sure what the issue with this our dev site, please help.