While attempting to run vxva (the volume manager GUI) with an upgrade from VXVM 2.0 or 2.1 to VXVM 2.3, you receive this message:
Volume Manager reports error: Configuration daemon can't speak protocol version
This message indicates that there is a version mismatch between the version of the volume manager daemon, vxconfigd, and the GUI, vxva, that you are trying to run. For example, you are running the 2.3 version of vxconfigd, and trying to run an old (2.1) version of vxva.
Most likely you are using the wrong path for vxva. For versions 2.1 and below of vxva, the binary can be found in /opt/vxva/bin; but starting with 2.1.1, the location was changed to /opt/SUNWvxva/bin.
If you did not remove the old SUNWvxva package before installing the new 2.3 version (which is normal, since you do not NEED to remove the old package), you probably still have the old /opt/vxva/bin in your $PATH, and, thus, you are attempting to run the older version of vxva.