It could be several things going on. There might be an issue with the drivers associated with your cable. It may be that E-scanner software isn't getting along with Windows 7.
You may first wish to confirm that you have all the USB to RS 232 drives installed.
Secondly, and I'm just trying this software out to see if I like it, but ScanControl seems to work with my Windows 7 (64 bit) and 780 scanner (not the exact model you have, but the same vintage of scanner). That seemed to be the only software I could get to program my 780, which I did last week.
(I had been using ARC 780 and really liked it, but it's not getting along with my computer and Butel says it won't be revised to work with my type of operating system, though my fingers are crossed that a change in heart my occur).
ScanControl Ver. 7.1