zone\client_packet.cpp, starting line 8303 (part of Client::FinishConnState2(...))
Code:
//validate adventure points, this cap is arbitrary
if(m_pp.ldon_points_guk < 0 || m_pp.ldon_points_guk > 0xFFFF) m_pp.ldon_points_guk = 0;
if(m_pp.ldon_points_mir < 0 || m_pp.ldon_points_mir > 0xFFFF) m_pp.ldon_points_mir = 0;
if(m_pp.ldon_points_mmc < 0 || m_pp.ldon_points_mmc > 0xFFFF) m_pp.ldon_points_mmc = 0;
if(m_pp.ldon_points_ruj < 0 || m_pp.ldon_points_ruj > 0xFFFF) m_pp.ldon_points_ruj = 0;
if(m_pp.ldon_points_tak < 0 || m_pp.ldon_points_tak > 0xFFFF) m_pp.ldon_points_tak = 0;
if(m_pp.ldon_points_available < 0 || m_pp.ldon_points_available > 0xFFFF) m_pp.ldon_points_available = 0;
Comment says arbitrary, and 0xffff is 65535.
As an aside, there's also an automatic skillup for swimming to 100 just below that.