Actually, I had this problem same as you. My windows is server 2008 and my subversion info is :
TortoiseSVN 1.7.6, Build 22632 - 64 Bit , 2012/03/08 18:29:39 Subversion 1.7.4, apr 1.4.5 apr-utils 1.3.12 neon 0.29.6 OpenSSL 1.0.0g 18 Jan 2012 zlib 1.2.5
I used this way and I solved this problem. I used [group] option. this option makes problem. I rewrite authz file contents. I remove group option. and I set one by one. I use well.
Thanks for reading.