VPN Problems - Specified network name is no longer available

Hi!

I recently installed a VPN router to a remote location. After successfull authentication and after mapping a drive I am able to browse my remote computer. All well. However when I try to copy any file larger than 1MB I get error "Cannot copy . Network name is no longer available." Now I read few articles regarding this issue and one ended up being the router so I changed the router but still the same thing. What puzzles me is that after receiving error I am still able to browse my mapped drive. Could it really be a WORKGROUP issue? There is no AD on remote location.

cheers,
Vlado