The last version of openssl has stricter rules for checking DER encoded ECDSA signatures.
Therefore, the peercoin clients dynamically linked to the last version of openssl will reject some blocks that will accepted by the other nodes, causing a network split.
So, if you compile your peercoin client yourself (without using gitian), don’t update openssl on your system, or patch the sources.
I ported the bitcoin core patches for this issue for Peerunity and made a pull request (https://github.com/Peerunity/Peerunity/pull/145).
This patch should also work for the Ppcoin sources, but I haven’t tested yet.
However, the binaries downloaded from peercoin.net are not concerned by this problem, because they use a statically linked embedded version of openssl.