L2 EoIP tunnel big problem with SMB share

Ho all,
I need anche help…
The scenario io:

  • n. 2 CCR 1009 both connected via FTTH link at 250 m bit/sec, wan address with PUB IP
  • n. 2 networks to bridge via L2 tunnel; both networks use 3 VLANS plus default VLAN (1)

I have setup a EoIP tunnel, all seeams to work well but when I try to copy a large file (like 50 Mb or more) from a Windows Server share across the L2tunnel the copy randomly interrupt and file copy fail.
Alla other networks service are ok.
Ping at 1500 bytes or more from site to site is OK with no packet loss and latentcy is about 3 ms.

Any help will Be very appreciated.

Thanks
Piero