Are you connecting the USB cable to your computer AFTER opening the USB on the 2488? here are the instructions:
1 With the transport stopped, from the DISK
menu, highlight USB OPEN/CLOSE, and press
ENTER.
2 The 2488 saves your data, restarts, and a
popup message appears.
While this popup is showing, you are “locked
out” of any operations on the 2488. It can only
be used as a USB disk.
3 Connect the 2488 to the personal computer.
4 Perform all USB operations with the personal
computer (file copy, etc.).
5 Disconnect the computer (you should first see
“The 2488 and USB” on page 73).
6 Press EXIT to close the USB and restart the
2488.