Why can't I change security settings for a share folder?

[Mizugori]

I am logged onto the server as administrator. I am trying to create several folders on one of the server drives, for use by different departments. So I made security groups for each department, and was planning to give each group access to their folder. I right-click on a folder (say IT), go to properties, sharing tab, check 'share this folder,' then security tab, only I cannot change the check boxes, they are greyed out. Why can't I change these? For example, for the IT folder I created, it lists:

Administrators (DOMAIN\administrators)
CREATOR OWNER
Everyone
SYSTEM
Users (DOMAIN\users)

and each of them have boxes checked under the allow column that I cannot change. I checked the effective permissions for the folder and sure enough, it says group 'everyone' can read the folder...

 

[Mizugori]

Ok what I did was to create one share folder with departmental subfolders inside. I set the share settings on the share to allow all authenticated users full access, then I tightened down the security settings on each subfolder. It works exactly as I wanted it to. I had to click on advanced on the security tab and remove inheritance (uncheck the inheritance checkbox and then click 'remove' in the prompt that follows) to get it to let me make my own perms from scratch.