This still seems to be slipping people’s minds when working with SharePoint permissions. It makes it very hard to troubleshoot your sites if you are not a Site Collection Administrator.
So check all the user groups on your sites, (Site Actions – Site Settings – People and Groups – Select Group – Settings – Group Settings).
In here, make sure that everyone can view the membership or you will constantly get an error message that says you don’t have access to this information. It will drive you mad in large environments where you don’t have super power rights. Make it easy for you as a Site Owner and future Site Owners to manage. Fix the settings accordingly to this: