I'm living a real nightmare with permissions on my target folder.

I set the privileges to my INSTALLDIR with IS 12:
Owner Administrators
RWX Administrators
RW Everyone
RW Users
Fine, but once I'm logon as user I got an access denied to the INSTALLDIR.
If I create manually another dir with exactly the same privileges, then I can access to it as simple user without problem.
Is there something wrong with the permissions set by IS or did I miss something??
I would be grateful for any help!!
Thank you