SVN returning Access Forbidden when upgrading to 1.8+ clients

Question

SVN is returning Access Forbidden when upgrading to 1.8+ clients

Our server is running:

Server: Apache/2.2.22 (Win32) SVN/1.7.8 mod_auth_sspi/1.0.4 DAV/2

and when I try to upgrade to any of the following clients they all give Access Forbidden:

AnkhSVN 2.5 
TortoiseSVN 1.8.1 through 1.8.3 (1.8.0.24401 works) 
Silk SVN 1.8.1 through 1.8.3-1 (1.8.0 works)

Update: AnkhSVN 2.4 no longer works now that I've updated my local repositories to 1.8

Answer 1

It turns out that newer versions of SVN started to capitalize the domain name. And our authz file containes all lower-case domain\username entries.