Cannot preview or open PDF attachment

When trying to preview a PDF attachment from a page, we get an error message in a yellow box that says the document cannot be displayed because it cannot load (see attachment).

When trying to 'view' the attachment from the attachments page, we are presented with another error message that tells us to file a bug.

To my knowledge this is the only time this has happened.

We can, however, download the PDF and are able to read it just fine.