I have no solution to this, but this also happens using the latest ASUS firmware. I have a Maxtor 300GB disk on my usb-port and when I try to copy a few GB to the disk, at some point it will fail and I have to restart the wl500gP . So, I guess it's not the Oleg firmware causing your problem.
By the way, the performance of this configuration is not optimal. I get max 2MB/s copying files to and from this HDD, about 25% of the performance I get when I connect the drive to an usb port on a PC. Any tricks anyone?