PDFs not showing in Attach File Panel?

Using EndNote X8, I have saved PDFs as File Attachments. However, when I click on the ‘Attach File’ button on the right hand panel, I am unable to view the PDF and a ‘Select a file to link to the reference’ dialog appears. If I then attach the PDF agian using this dialog (so a second copy is added), once I click out of the reference and save the changes the PDFs are indexed again. But then when I try to view the PDF in the right hand tab I have to go through the same process of selcting a file to link to the reference?

Thank you - now I feel foolish.