HPUX swinstall Cannot establish a lock on this target because of an external error

After your register your depot:

# swreg -l depot /dir/to/my/depot

And you try to install install you get the error in /var/adm/sw/swinstall.log or as std out:

ERROR:   "my_host:/dir/to/my/depot":  Cannot establish a lock on this
         target because of an external error (for example, the lock
         file could not be created).

Try this:

# cd /dir/to/my/depot/catalog
# touch swlock 
# chmod 666 swlock
# swagentd -r

Now swinstall should work.