Discarding conflicting packet due to recent request

i am receiving this error from time to time in the radius log Error: Discarding conflicting packet from client PPPOE1 port 33184 - ID: 1 due to recent request i searched online and found very old posts about this error, what does it mean? is it something related to the database slow? or broken NAS? my NAS is a Linux server running accel-ppp as a pppoe-server. is this something related to the NAS itself or to my configuration with freeradius? also what does this error means? Regards.