Hi Daniel, We found the mistakes : 1-  there is a bad STP configuration between the N2048 stacks and the core (Alcatel Lucent OS6850) that makes some re-convergences. This explains the loss packets and the error message like    OSAPI[ipMapProcessing]: osapi_net.c(1381) %% osapiArpFlush: could not get interface Vl1061! errno = 19 It is a pity that the message is not more explicit (no STP message, no STP error on N2048)  We do not understand why the first stack works while the others do not work... 2- as I mentioned in my private message, the RADIUS error came from missing instructions (perhaps loss after a reboot without saving the conf). This morning all is fine. We will deploy the user's VLAN. Once again, the problem was between the chair and the keyboard... Thank you for everything. 
Hi,I have 3 N2048P stacks connected to a central switch with Giga SFP. The 3 stacks have the same config and the same firmware 6.3.2.7All the 3 links are up without any error on the central switch.I can connect to 1 stack without error (local account or radius account).I can connect to the 2nd stack, but with error (local account only, no radius) : 53% ping packets loss.I can't connect to the 3rd stack : 100% packets lossMy syslog server receive some errors for the 2nd stack and a lot of error for the 3rd :OSAPI[ipMapProcessing]: osapi_net.c(1381) %% osapiArpFlush: could not get interface Vl1061! errno = 19  (the vlan 1061 is the admin vlan).  What is that error ipMapProcessing / osapiArpFlush: could not get interface Vl1061! errno = 19 ?  Is it a hardware problem : stack ? SFP uplink ? Fiber ? Is it a configuration problem ?  Thanks for your answers.  Best regards. 
N2048P stack unreachable - ipMapProcessing / osapiArpFlush error