Assist Unattended access from Mac to Mac grey screen

I have had remote access to a customer Mac OS system from my MacBook. After setting up Unattended access the session won't start, showing a grey screen.

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Release Notes: Version 1.91, February 2015
Unattended Access (Beta) is live! Unattended Access, a feature requested by a lot of our customers is live now. Currently, it's in beta. You can add up to 100 computers per Technician subscription. They can also be accessed by your organization members. My Computers list in Zoho Assist home page will always display the online status of your unattended computers. You can rename the computers whenever you wish. Currently, Unattended Access can be configured only for Windows computers. Nevertheless,