If you are asked to re-authenticate a machine, even after the owner has authenticated it, take the following steps:
Ensure that the browser cookies were not deleted while clearing the browsing history (authentication credentials are stored in the form of cookies).
Read: Browser Settings for Machine Authentication.
Check your antivirus software settings.
If your computer has any antivirus software installed such as CCleaner, ensure it does not remove the flash player data stored on your computer.
Also, ensure that your Zenoti business URL (example: http://xyz.zenoti.com/) is in the exception list. This ensures that the cookies are not deleted and the information is stored on the computer.