svnsync errors out on trying to sync a revision that adds or changes a mergeinfo property containing a reference to revision number 0.
Such mergeinfo is now considered invalid, and cannot be committed with recent servers, but can be committed through a server older than 1.6.18 for HTTP or older than 1.6.17 for the other protocols. See issue
SVN-3895 "repos layer does not verify mergeinfo syntax".
In addition, svnadmin dump errors out when it tries to dump such a property, iff any non-zero start revision is specified for the dump.
I have confirmed this, testing by hand, using Subversion v1.7.16 and v1.8.8.
Email thread: "Mergeinfo containing r0 makes svnsync and svnadmin dump fail" from Julian Foad on 2014-03-03, archived at e.g. <http://svn.haxx.se/dev/archive-2014-03/0030.shtml> or <http://mail-archives.apache.org/mod_mbox/subversion-dev/201403.mbox/%3C1393863884.78994.YahooMailNeo@web87703.mail.ir2.yahoo.com%3E>.