The RE4 fix was specific to the RE4 cable, and will not help here. Also, we've used the same FTDI drivers since 2009, so upgrading versions should not make any difference.
The assumption always has been in Windows that newer versions of a program are always better, and they will get installed and overwrite any previous versions. For applications, this makes sense, but for shared drivers there is no advantage to upgrading the driver if everything is working correctly. The problem we've found is that other hardware devices also use the FTDI drivers, and can overwrite the FTDI USB drivers with a newer version. In theory this is all fine and well, but FTDI drivers are not always backwards compatible, and/or have bugs, which is what the RE4 cable problem was caused by. I contacted FTDI about this but they would not fix the bug. A compounding problem is that Windows does not fully uninstall a USB driver when you uninstall it. Also it may be difficult to track down what other hardware devices use the same drivers.
Here's what I suggest: These all assume a certain level of PC know how.
Open the device manager, find the s300 USB device, and open the properties. The driver version should be 2.4.6.0 and the date should be 3/13/2008, otherwise it has been updated. Post what you see here.
Uninstall the drivers method #1. Create an environment variable devmgr_show_nonpresent_devices=1 from System Properties -> Advanced -> Environment Variables. Open the device manager, under View select 'Show Hidden Devices'. Under the USB controllers rich click and uninstall all the S300 / KPro etc devices. On Windows 7, select the 'uninstall driver' option too.
Uninstall the drivers method #2. Download and install the RE4 fix from
http://hondata.com/updates/FTDIUSBFixSetup.exe. After installation, from the start menu run (as administrator) the 'FTDI Driver Clean' application. After is has run, uninstall the RE4 fix.
Uninstall the drivers method #3. Under Windows/Inf do a search for oem*.inf containing Hondata. Delete the .inf files and the .pnf file of the same base name.
Uninstall the drivers method #4. Under Windows/System32/Drivers delete FTD2XX.sys and ftdibus.sys files.
Reboot, make sure only the latest version of SManager is installed, then connect the s300. When prompted, don't allow Windows to look online and direct it to the SManager installation directory.
Hope this makes sense. Good luck.