Clicking on 'Add Link' takes me to the 'Posts' page!

Hello all,

Is anyone able to explain what may be the cause of this? We are running 3.7, and have been since it’s release.

Whilst attempting to add a link for a specific piece of test on a page, when clicking ‘Add Link’, I am then taken to the ‘Posts’ page – why is this happening?!

Many thanks.