Remote Desktop 2: "Didn‘t upgrade to version 2.1"

When using the Upgrade Client Software feature from the Manage Menu in the Remote Desktop admin application, you may encounter this alert message:

"Failed on all. Didn't upgrade to version 2.1."

Additionally /var/log/system.log on the client computer contains this entry:

localhost /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/MacOS
ARDAgent: CheckDestination: Package install folder is invalid.

Solution

This is caused by incorrect permissions of the /private/tmp folder, which should be owned by root with a group of wheel:

drwxrwxrwt 12 root wheel 408 14 Oct 13:35 /private/tmp

You can use Disk Utility to repair the permissions of an affected computer's system volume. Alternatively, you can execute the following command on the affected client systems:

sudo chown root:wheel /private/tmp