This release fixes entropy bit calculation problem, which was discovered yesterday.
Sources: https://github.com/CryptoManiac/novacoin/
Binary builds: https://sourceforge.net/projects/novacoin/files/
You need to update your nodes as soon as possible, otherwise you risk to be affected by blockchain fork which will happen soon (deadline is approximately ~30.03.2013) for unfixed clients.
P.S. Thanks to SunnyKing for help with investigating this issue. Smiley