P2pool was updated. It’s neccessary to apply this update after majority of hashing power upgraded. It fixes coinbase size calculation inaccuracy, which caused generation of invalid blocks in some cases.
Sources:
https://github.com/CryptoManiac/p2pool
Win32 py2exe:
http://sourceforge.net/projects/novacoin/files/p2pool_win32_py2exe_12_f.zip/download
