This might not be in the correct category. I have a pr4100 with 2 cameras working fine, I see now that the relationship between WD & Milestone Arcus has ended. Many users have written about their frustration in getting additional licences with no luck. I see that Amazon sell licences on the following link. Milestone Arcus Surveillance Camera Licenses - 1 Camera https://www.amazon.co.uk/dp/B016OJSSAO/ref=cm_sw_r_cp_taa_jPIbDbCF82ZR3. Why it takes 1 to 3 months delivery I can’t begin to guess. Has anyone used one of these licences and did it work.