The option to convert the disk from basic to dynamic is unavailable in Disk Manager after you configure a disk that is recognized by Windows 2000 or Windows Server 2003 to be a server cluster disk resource.
Users receive Access Denied when performing a certain action even though they appear to have the appropriate permissions. ECS can repro with a Test Account on the customer's Site Collection mimicking the customer's permissions, but not on other Site Collections (such as a test Site Collection).