PPTP encoding problem

i have a wireless network using mikrotik 2.9.7 with radius authentication, users dialing from windows xp using pptp,l2tp or pppoe are connecting normally and have access to the internet.
users connecting using a router such as dlink:

  • if the router is using pppoe everything is ok
  • if the router is configured to use pptp, i can c that the user has logged in but he can’t access the internet.
    i’ve noticed that the router’s users are connecting without encoding.
    the pppoe without encodind is working fine but not the pptp.
    any suggestions ?
    thx in advance