Immediately after installing Leap 42.1 on my hp laptop, "zypper up" complained with
Refreshing <repo names>
Cannot write file '/var/adm/mount/AP_hdgfyx'
Of course, this directory was okay and writable, root partition was not filled up, cleaning up by rm /var/adm/mount/* didn't help, either...

To cut a long story short: I could get rid of that error by cleaning up all repositories' metadata and refreshing it by running
# zypper cc -a
# zypper refresh
After that, "zypper up" went well.

As I couldn't find any occurence of this problem anwhere else, I thought it worth to be mentioned (and to be searchable) here.
Hope this helps anyone out there.