Why can't I read a file when I have group permissions

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http://stackoverflow.com – I have created a new admin group which I am a member of. I have changed permissions of the file test_admin.txt so that it can only be read and written by members of this group: ls -a returns ----rw---- 1 joe.bloggs admin 37 Feb 6 16:49 test_admin.txt groups joe.bloggs returns joe.bloggs : linkmed admin I have logged out and back in as suggested by Why can't I write eventhough I have group permissions? but I still receive the same error message test_admin.txt: Permission denied What am I doing wrong? (HowTos)