Following up...
pptp problem might also be linked to affa.
When a client tries to connect during an affa scheduled job, this error occurs:
Dec 16 16:00:08 serveur /sbin/e-smith/affa[25061]:.../users2affa: ...|valid|yes
Dec 16 16:01:35 serveur pptpd[25149]: CTRL: Client 192.197.166.31 control connection started
Dec 16 16:01:35 serveur pptpd[25149]: CTRL: Starting call (launching pppd, opening GRE)
Dec 16 16:01:35 serveur pppd[25150]: Plugin radius.so loaded.
Dec 16 16:01:35 serveur pppd[25150]: RADIUS plugin initialized.
Dec 16 16:01:35 serveur pppd[25150]: pppd 2.4.4 started by root, uid 0
Dec 16 16:01:35 serveur kernel: divert: not allocating divert_blk for non-ethernet device ppp0
Dec 16 16:01:35 serveur pppd[25150]: Using interface ppp0
Dec 16 16:01:35 serveur pppd[25150]: Connect: ppp0 <--> /dev/pts/2
Dec 16 16:01:35 serveur pptpd[25149]: GRE: read(fd=7,buffer=8056600,len=8260) from network failed: status = -1 error = Protocol not available
Dec 16 16:01:35 serveur pptpd[25149]: CTRL: GRE read or PTY write failed (gre,pty)=(7,6)
Dec 16 16:01:35 serveur pptpd[25149]: CTRL: Reaping child PPP[25150]
Dec 16 16:01:35 serveur pppd[25150]: Modem hangup
Dec 16 16:01:35 serveur pppd[25150]: Connection terminated.
Dec 16 16:01:35 serveur kernel: divert: no divert_blk to free, ppp0 not ethernet
Dec 16 16:01:35 serveur pppd[25150]: Exit.