Update: Apple released a second version of ARD 3.6.1 on September 24. The version number hasn’t changed. Give it a try if you had issues connecting with Screens and let us know if it fixes the issue. http://support.apple.com/kb/DL1594.
In a nutshell, this issue will occur when a VNC app (including Apple’s own Screen Sharing app) tries to wake a sleeping computer.
This issue affects all VNC clients. We notified Apple on several occasions and even though they’ve acknowledged the issue, unfortunately it still hasn’t been fixed and we have no idea when it will.
However, there are two workarounds that you should try:
The trick here is to use a SSH session to wake a sleeping Mac. Once the computer is awake, initiating a VNC connection should work just fine.
To enable SSH in Screens and your Mac, scroll down to Optional: Securing your Connection in this document.
You can enable SSH in Screens for Mac by selecting a screen and edit its settings:
You’ll find more details in the Screens for Mac documentation.
Important: Do not enable “Disable SSH tunneling on local network” as it may prevent the SSH session to initiate if you’re on the same local network and Screens detected your Mac.
As for Screens Connect, simply open the preference pane in System Preferences and click on “Use SSH tunneling”:
Screens Connect will enable Remote Login automatically if it is not already enabled (System Preferences → Sharing).
You’ll find these instructions in the bundled documentation for all 3 apps.
One caveat: using a SSH tunnel will slow things down a little since the data will be encrypted.
Prevent your computer from sleeping
This is a less optimal solution but if the first workaround doesn’t work for you, then you should consider this one until Apple fixes the issue.
To do so, open the Screens Connect preference pane in System Preferences and click on “Prevent computer from sleeping”.
If you use TouchPad or NumPad, the only solution for now is either manually wake your computer (by click with the mouse or hitting a key on your keyboard for example) or set your computer not to sleep:
Keep your Mac updated!
We also recommend that you keep OS X updated to the latest version. If you haven’t updated Apple Remote Desktop Admin, then we advise not to until Apple release version 3.6.2 or whatever version comes next. We will keep you informed of the issue resolution.