What is /tmp/appserr?
It's a log file for tce-load to check whether an extension was mounted correctly.
Perhaps you had ran tce-load as tc before switching to "newuser"
Since the file was created before switching to superuser, (permission rw-r--r-- tc:staff)
making the file unwritable for "newuser".
A bug for tce-load I think, it woud be better if the permission was set to rw-rw-r-- root:staff
Just delete the file and it should be good to go.