When VMware released VM hardware version 10 for vSphere 5.5, it didn’t take into account the number of users using the free version of the hypervisor. These folks who upgraded their VM hardware to version 10, found themselves unable to edit the settings of the VM post upgrade.
The only option was to to edit it via the Web client, which was not available to the free hypervisor users. There was a workaround to downgrade it to version 9, however this was a troublesome workaround at best and caused a lot of grief.
So now VMware has fixed it with the release of vSphere 5.5 Update 2. Take a look at the  following blog from VMware:
VMware Blogs
This is good news indeed!