This message is displayed if the server response is truncated (the data sent from the server gets corrupted). This could be because:
1) The license file has been corrupted.
Register using the license contained in the zip file. If you have not been sent a zip file containing your license then ask the Publisher (company that supplied the document) for one.
Before registering again you will remove your keystore. Once you have done this double-click on the license file to register again.
2) A proxy is in use and proxy settings have not been configured in the viewer software.
Proxy settings can be configured in our software from the Windows Start menu >> All Programs >> LockLizard >> Safeguard >> PDF Viewer >> Proxy Settings).
For more information on Proxy settings please see Proxy Settings.
3) Your firewall or ISP has prevented you from accessing the administration server using HTTPS.
If this is the case, ask the Publisher to send you a license file that uses HTTP to connect to the licensing server instead.
If you are clicking on the link in the email to register instead of an attachment then copy the link URL into your browser and change the HTTPS to HTTP in your browser’s address bar.
In either case above, before registering again you will need to remove your keystore.
If none of the above work, it could be that your customer account is corrupted. The publisher will need to delete and re-create the customer account on their admin system and then send you your new license file details.