vpn not correct working

Hi all

First sorry for my english its not my main language.:o
I have upgraded from my rtn66u(firmeware 3.0.0.4.374.34_2) to AC68u(firmware RT-AC68U_3.0.0.4_374.37_0)and the problem is with the ac68u the VPN PPTP is not correct working!
1 ) the connection is working without any issues only i can not connect to network drives as example :mybooklive or Qnap 419 P .(error message server not found)
2) i have flashed other firmewares from merlin and asus no change to connect the network drives over the VPN with the router AC68u)
3) i have compared the settings from my old router (rtn66u) all settings are the same and the VPN is working fine with my old router !

here is the logfile from the router the strange thing is i have the same error message in the rtn66u and ac68 pls note on my old router the rtn66u the vpn working great.

Log :
Jan 9 18:26:49 pptp[1049]: Using interface ppp10
Jan 9 18:26:49 pptp[1049]: Connect: ppp10 <--> pptp (194.230.155.210)
Jan 9 18:26:53 pptp[1049]: MPPE 128-bit stateless compression enabled
Jan 9 18:26:56 pptp[1049]: Cannot determine ethernet address for proxy ARP

Anyone idea what is wrong with the ac68u or the firmeware.
I think in this case is not the error message the reason because both device has this error message and the RTN66u Works perfect.

thank you very much for your help.