Assuming your running on Windows XP 32 bit....
This worked for me...
Leave the scope attached to the PC, then right click on 'My Computer' and select 'manage', the select 'device manager' and look for a device under 'USB' which has yellow bang ("!") against it. Right click this and select 'uninstall'.
Now remove the scope from the PC and install the software.
Attach the scope at the appropriate time.
I hope this helps.