The Installation/Registration error is almost always caused by a permissions problem for the client.  

The most common cause is that the client has been installed as a normal user but to the wrong location on the system.

The Privia client can be installed to two locations on a system.  Normally the location is automatically chosen based on the user type runs the installer.  But some users may have elevated permissions that causes the installer to install to a different location.

The normal mode of installation is to run the client installer as a user of a system.  This installs the Privia Client to c:\users\USERNAME\ProgramFiles\Privia and creates the initialization information in that same location.  When installed this way, the client is installed just for that single user and all of the registry information for the client is written to HKCU.

The alternative mode of installation is to run the client installer as an administrator by right clicking on the installer and choosing the option to "Run as Administrator".  This runs the client with elevated privileges so that it can write to c:\Program Files (x86).  This installation method is intended to be used on systems which have users that share the computer.  When installed this way, both the program and the initialization information is written to c:\Program Files (x86)\Privia AND registry information is written to HKDU.

The "tell" for how the client was installed is whether there is an icon on the desktop for users for "Launch Privia".  If there is a Launch Privia icon on each user's desktop it has been installed with the alternative method.  In this case, the end user must run the "Launch Privia" link at least once so that the registry information is copied from HKDU to HKCU and the necessary structure is built out for the profile cache in c:\Users\USERNAME\AppData\Roaming\Privia.

The problem occurs when a user installs the client and the installer identifies the user as having administrator rights on the system so that it writes the installation files to c:\Program Files (x86)\Privia but creates the registry information in HKCU instead of HKDU.  When the client tries to run, the cache area is not properly built out and the permissions on the DLLs for the application are incorrectly set.

There are two things to try in this situation.

1) Reinstall the client but during the installation, make sure that it is installing to the proper location (e.g. if installing as a user, it should install to c:\Users\USERNAME\ProgramFiles\Privia).  During the installation, override the installation location if it choose c:\Program Files (x86) and the application should run properly.

2) Reinstall the client by right clicking on the installer and choosing "Run as Administrator".  Then have the end user run the "Launch Privia" icon at least once to create the proper registry information.

If option #1 doesn't work, option #2 almost always corrects the problem.