Whether you are Domain Admin or Local Admin does not matter, it is role membership in SSRS that matters ie member of System Administrator role.
BUILTIN\Administrators is added to the System Administrator role during setup so local admin should have access to site settings.
It may be someone has removed or changed BUILTIN\Administrators role permission
On the SSRS server try running browser as Administrator
Or refer to http://stackoverflow.com/questions/707219/lost-ability-to-be-admin-on-sql-server-reporting-services-2005
Far away is close at hand in the images of elsewhere.
Anon.