XF 1.1 Attachments Not being Crawled

My webmaster tools account shows almost all the attachments in the threads / posts as giving an error code of 403.

I tried checking the htaccess file and everything seems to be normal there.

From a browser they are not showing any '403 forbidden error', however Google seems to be forbidden.

Any suggestions on how to resolve this, as this means my images will not get indexed and not show up in 'Image Search'.

A screenshot of the 'crawler error' in webmaster tools is placed below: