I'm successfully using the Wiki plugin on my site and all

Hi,

I'm successfully using the Wiki plugin on my site and all is great, except I just noticed that only the admin can upload images with the media uploader. The add media options are there for the custom role I created 'Expert', but when uploading the images they fail and I get the error message as you can see here;

http://thehive.hivemindnetwork.com/wikidocs/hivemind-internal-documentation/

I have the user role editor plugin installed and with setting enabling the role 'Expert' to upload files as shown here;

http://thehive.hivemindnetwork.com/wikidocs/hivemind-internal-documentation/

The settings on my uploads dir are as follows;

drwxrwxr-x 15 www-data www-data 4096 2014-04-28 16:55 uploads

What am I missing? I can upload media fine as admin but not as role 'Expert'. I was sure this was working but now it isn't. I will also grant support access to the site for you now but please be careful as this is a live production site.

Thanks