This error message probably has nothing at all to do with the user's system PROM version. It most likely is related to the fact that the file /dev/vx/config (and the pseudo device that it is linked to) does not exist on the system. A few things could contribute to this file not being created:
Make sure these lines are in the /etc/system file:
forceload: drv/vxdmp (only needed for SEVM 2.5 and above) forceload: drv/vxio forceload: drv/vxspec |
Make sure the vx entries are in the /etc/name_to_major file.
grep vx /etc/name_to_major |
If you have not performed a boot -r since doing a pkgadd to the Volume Manager software, this might have contributed to the problem.