Could not save the list changes to the server. This list cannot be deleted.

When SharePoint 2010 list becomes unavailable to delete.

error message: Could not save the list changes to the server. This list cannot be deleted.

solution: run powershell command as administrator type-in the ff:

$web = Get-SPWeb http://yourserver
$list = $web.Lists["MyList"]
$list.AllowDeletion = $True
$list.Update()

Now go to your list settings again and you'll see the delete command or you can just run the line below:

$list.Delete()

hope that helps!