That's the error if I download the .zip from github and attempt to build, after syncing in the SPL, RakLib and Lang libraries from the following sources: https://github.com/PocketMine/RakLib/archive/master.zip https://github.com/PocketMine/PocketMine-SPL/archive/master.zip https://github.com/pmmp/PocketMine-Language/archive/master.zip Where are you guys getting a newer version of RakLib with this missing PacketReliability library? Using the poggit script provided in another thread here, the .phar file was built with the missing library: [ raklib]# ls protocol/ | more ACK.php ADVERTISE_SYSTEM.php AcknowledgePacket.php CLIENT_CONNECT_DataPacket.php CLIENT_DISCONNECT_DataPacket.php CLIENT_HANDSHAKE_DataPacket.php DATA_PACKET_0.php DATA_PACKET_1.php DATA_PACKET_2.php DATA_PACKET_3.php DATA_PACKET_4.php DATA_PACKET_5.php DATA_PACKET_6.php DATA_PACKET_7.php DATA_PACKET_8.php DATA_PACKET_9.php DATA_PACKET_A.php DATA_PACKET_B.php DATA_PACKET_C.php DATA_PACKET_D.php DATA_PACKET_E.php DATA_PACKET_F.php DataPacket.php EncapsulatedPacket.php NACK.php OPEN_CONNECTION_REPLY_1.php OPEN_CONNECTION_REPLY_2.php OPEN_CONNECTION_REQUEST_1.php OPEN_CONNECTION_REQUEST_2.php PING_DataPacket.php PONG_DataPacket.php Packet.php PacketReliability.php SERVER_HANDSHAKE_DataPacket.php UNCONNECTED_PING.php UNCONNECTED_PING_OPEN_CONNECTIONS.php UNCONNECTED_PONG.php TIA