[Plugin: User Access Manager] Lock files is not working

I’ve just created a new wordpress test system with the only additional plugin being User Access Manager Version 1.1.2. I have turned on permalinks. Everything seems to work except Lock Files. I have Lock Files set to yes and Download Type set to fopen. After doing this I uploaded an image by adding it to the Media Library.

The image loads OK but the thumbnail does not appear in the Media Library.

When I edit the post and add the image I can see it in the post. However when viewing the site the image does not show, even for the administrator.

If you like I can give you admin access to the test site.