• License Server Operation Failed error message. What can I do?

This error means that your copy of FlippingBook Publisher could not connect to our servers. The best way to resolve this depends on the circumstances. So if you get this notification:

Please choose what’s relevant to you:



1.If you have version older than 2.6.5. The problem is connected to a change in the SSL/TLS certificates on our license servers and due to that change, some older versions of Publisher can't connect. If your version of FlippingBook Publisher is older than 2.6.5. and you get "License server operation failed" error message, please, contact us at support@flippingbook.com or use our contact form. We will be glad to fix this issue for you.

You can check what version of FlippingBook Publisher you have if you go to your personal account and login with your FlippingBook credentials.

2.If you have not used the software earlier on this network, then the network may use a proxy server. Proxy server might have to be configured to allow access. Ask your IT administrator to check that the following addresses are available in your network. If they are blocked, ask to add them to the whitelist:

Please give this to IT administrator to whitelist:

Two ports are used: 80 and 443.

  • publisher.flippingbook.com:80
  • publisher.flippingbook.com:443
  • logon.flippingbook.com:80
  • logon.flippingbook.com:443
  • backend.cld.bz:80
  • backend.cld.bz:443
  • backend.cld.bz:20000
  • backend.cld.bz:20001
  • backend.cld.bz:20002
  • static.flippingbook.com:80
  • static.flippingbook.com:443
  • flippingbook.com
  • pay.flippingbook.com
  • stats.flippingbook.com
  • account.flippingbook.com
  • secure.flippingbook.com
  • cld.bz
  • pages.cld.bz



 3.If you have earlier used the software on this network, but not on this computer, then you will have to enter your proxy settings.

Please click on the Settings button in the login screen. Then change the Connection to Automatic. It might help because it looks at the general proxy connection settings for the internet connection. Even if you don’t know what the proxy settings are, this setting can discover the correct proxy settings.

Or to Custom Proxy Server (if you know the proxy credentials)

and then press Check connection button to verify if you can reach our servers.

Note! In older versions of FlippingBook Publisher you may not have this window. You will see a notification whether your connection is successful or not.



4.If you have earlier used the software on this computer, then it is also possible that it uses old server data.

 To delete this, please do the following:

  • Press the Windows-key and the R-key at the same time.
  • In the opened field type %temp% and press Enter.
  • Find the CachedServiceDiscovery.xml file
  • Close all Publisher windows
  • Delete the file

  • Start FlippingBook Publisher again.

This helps because the file contains connection settings that are specific to a particular edition of Publisher. In some cases FlippingBook  Publisher doesn't recognize that this file contains settings that are for an older version. This makes the connection fail. For instance it happens sometimes after upgrade.

If you’ve followed all the steps and still cannot connect, then something is still blocking the connection to our licence server. Contact your IT administrator and show this article.

If any further help is required, please contact us with a screenshot of the error message and the steps you have already tried.

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