We have diagnosed the issue and found 2 causes:

1. Installing the client before download completes. The system may believe the client has completed downloading even if it is only 99% complete. When this happens, the system determines that the process has completed instead of sending an error message. To resolve this issue, please re-download and install the completed client.

2. Viruses can corrupt files during installation. Please scan your computer and remove any threats to your computer. Please keep in mind, however, this is a very rare issue. 

Link to downloader:

http://redfox.cdn.playredfox.net/redfox/cdn/game_client/downloader/v1002/Downloader.exe