This error means that you need to re-register your license:
- On your iPad, go to the PDCViewer app and tap the gear in the top left corner.
- On the settings screen, choose the "Remove Keystore" option and confirm your choice.
- Open your Safari app and return to the Download Center on our website.
- Skip to Step 3: License Registration, select "Register this device" next to your iPad, then choose the option to "Open in PDCViewer."
- Tap on the latest license listed in your PDCViewer's licenses area and you should receive a successful registration message.
You should now be able to open files on your iPad.