Today I have seen this issue and it took while before the problem was solved.
What preceded was an uninstallation of Exchange 2007 organization and before that I moved all Public Folders to Exchange 2010 Server. After these tasks I needed to change some of the settings of the Exchange hybrid configuration and there you go.
ERROR:Updating hybrid configuration failed with error ‘Subtask ValidateConfiguration execution failed: Configure Legacy Exchange Support at Microsoft.Exchange.Management.Hybrid.Engine.ExecuteTask(TaskBase taskBase, TaskContext taskContext)
When using the verbose switch there are messages like Get-PublicFolder -Identity '\NON_IPM_SUBTREE\SCHEDULE+ FREE BUSY' -Server 'Your Server Name' -recurse
It looks like Exchange is finding some old configuration because it's claiming legacy exchange support. The only thing what was changed was the location of Public Folders and ofdfcourse the decommissioning of Exchange 2007.
The solution was not more than running the folowing command on the Exchange Servers where the Public Folders resides.
Run the install cmdlet . To do this user need to launch Windows Powershell (not the Exchange Management Shell) and then run the commands as below:
- Start powershell.exe
- add-pssnapin Microsoft.Exchange.Management.PowerShell.Setup
- install-freebusyfolder -verbose
Now re-run the Hybrid Configuration Wizard from the On-Premise mailbox server. User should not receive the above errors now.
Original article for the solution is found here