I believe when starting Tableau Prep errors can occur if its in an environment where a proxy server is used.
It might be worth trying the following...
Ensure that localhost (127.0.0.1) is added to the exception list in your computer's proxy settings. To do so, follow the steps below with the help of your IT team:
- In Internet Explorer, navigate to the Tools menu (cog icon), and select Internet Options.
- On the Connections tab, click LAN Settings.
- If a proxy server is enabled, check the box marked Bypass proxy server for local addresses.
- If Automatically detect settings or Use automatic configuration script is enabled, work with your local IT team to bypass 127.0.0.1 addresses in the local proxy by clicking Advanced and manually add 127.0.0.1 in Exceptions field.