Apps not appearing in iTunes

I did a search, and the only advice I found instructed me to go under File, Devices and download apps.

I get an error 'Cannot write to disk (-54)' and no transfer. This is recent, as before the update, all apps were listed in iTunes. This true for both my iPhone6 and my iPad Air 2

It shows the page layouts with the apps on them, just no list of apps on the left side of the pages.

Any ideas?

Thanks,
Michael