When Installing Exchange from the command line in a locked down environment I was presented with the following error message on the CAS prerequisites check.
You must be a member of the 'Organization Management' role group or 'Enterprise Admins' group to continue.
When I checked the Organization Management members list, I didn't see my account there but when opening one of the groups that were member I was listed.
One of my first thoughts was, to check if I needed to be a member of the exact group and not a subgroup.
and of course this was the case, so if you run into this issue you need to get yourself added to the Organization Management group directly.
For some organizations this might cause some trouble since they have strict procedures around adding accounts to groups like Organization Management. But at least now you have some proof that hopefully helps