"ERROR: Failed to read INST_RELEASE file from target boot environment."

 I am attempting to install the latest Recommended patchset on a SunBlade 1000 running Solaris 10. When I execute

  installpatchset --s10patchset

I get the following error:

 ERROR: Failed to read INST_RELEASE file from target boot environment. This file

       must be present for patch set installation.

I've done some research on the net, and figured out that this is generally associated with having alternate boot environments, which this machine does not have. I also found a reference to a file that should be located in /var/sadm, but on this system, /var/sadm is a link to /tmp/sadm, which doesn't exist.