UsbServer stuck on RPi when copying large files

I installed USB Server on RPi and USB Client on Win7. We have an application that copies files from Win7 to a device connected to the RPi using USB protocol. We noticed that it works fine with small files, but fails when copying files with size ~ 1M. The Usb Server stuck and restart required to continue working with the USB Server. I tried to run it from command line with -d -o switches, but there are no messages that could help investigating this failure.

How this issue can be solved?

Thanks,
Leonid.