Two things you could try:
Option A:
1) Stop PGPTray process by right clicking on the PGP Tray icon and selecting "Exit PGP Services"
2) Open up My Computer on the computer that is not showing up on the server and delete the PGPprefs.xml and PGPPolicy.xml files from the %appdata\PGP Corporation directory.
3) Re-launch the PGPtray.exe from Start --> All Programs --> Startup
4) Fill in the users LDAP credentials for enrollment again
5) Right-Click on the PGP Tray icon in the system tray. Then left click on "Update Policy" once the client is done enrolling.
6) Check to see if that device updated on the PGP Universal Server and is now showing up.
7) If not, check the client logs under Reporting --> Logs on the PGP Universal Server and select ERROR from the drop-down instead of INFO. See if there are any errors being reported there for that client (it will list them client communications ID# by IP address and username there)
Option B:
Obtain SSH access to the PGP Universal Server and run the following query:
psql oviddb ovidr -x -c "select * from client_machine where hostname = 'FQDN_OF_COMPUTER_NAME_HERE';"
example:
computer name of pc is: test.example.com
query:
psql oviddb ovidr -x -c "select * from client_machine where hostname = 'test.example.com';"
If this returns a result, then there is information still stored in the database for that machine. It's just not showing up in the UI for some reason (UI resource issue, or possibly null data in the record somewhere)
Maybe that helps? At least for initial discovery to see what the problem is.