Security Tab settings in folders not applying

hi,

our file server is running on Windows 2008 R2 and we are having security issues with the shared folders.  when we try to provide access for the users in the Security Tab, they are still unable to read or write even if they already have full control of the folder unless we add them in the Advanced Sharing permissions.  it's like the Security Tab has no bearing with regards to security.  only the permissions in the Advanced Sharing allow them to access the folder whether read or write and or  by adding "Everyone" which should not be the case.

any thoughts on this issue?

thanks.