SVN checkout ends with unknown revision -1 if ra_serf library is used. Have a look at https://groups.google.com/forum/?fromgroups#!topic/scmmanager/JKI2TNqkvgg
Note: The version above shows an error (E175009: Unknown tag 'txdelta' while at state 4) durring the update command. But the same error is shown on a mod_dav_svn 1.6.16 with a client in version 1.7.5.
There seems to be a bug in the subversion client, which causes the "txdelta" error. Have a look at http://old.nabble.com/Patch-to-remove-libsvn_ra_neon-td33999221.html
This is also interesting http://subversion.tigris.org/issues/show_bug.cgi?id=3990
With the test version scm-server-app-2012081301.zip and subversion 1.7.6, all functions seems to work. It is possible that you test this.
Opened a ticket at svnkit:
The new version of the patch svnkit-dav.ra_serf, seems to fix the ra_serf support.
The patch will be included in version 1.32 of SCM-Manager.
Version 1.31 of SCM-Manager with svnkit-dav.ra_serf patch:
Issue #406 was marked as a duplicate of this issue.