Insert/edit link button- error

Recently the box that appears when insert/edit link button is pressed in visual editor just displays the home page of my site instead of the options for inserting or editing a link.
Can still add link in html view but my clients who manage this site have very limited ability with html.
I’ve tried deactivating all of the plugins which made no difference.
I haven’t been able to find any documentation of this issue, except for similar problem which was due to a firefox addon, which was not in my case…