The rake task 'fix_db_cache' triggers CacheManager, and CacheManager tries to find roles, user groups, etc.. without any permissions. This will cause it to fail with an error similar to https://gist.github.com/52da11cb368ec530bcf0247d3ee38855 .

Many of the actions called by CacheManager, like UsergroupMember.save will have to find objects that needs permissions to be viewed, hence CacheManager has to be called "as_admin".