Access Denied. I need to change (reset) permissions.

I have a shared folder which is on a server running server 2008 standard.  For some reason the permissions to several sub folders have changed and I cannot access them.  I go to the parent folder and try to take ownership of the folder but access is denied to the sub folders.  Same "access denied" error when I try forcing permissions from parent folder to all descendants.

Any suggestions on how I can force a change of permissions to these sub folders?

Regards,

Graham.