Are you downloading the V300 with the serial cable you used for the live telemetry, or a memory cartridge?
If you are using the memory cartridge, check to see which version of Windows Vista you have. Recently, Microsoft has been pushing the 64-bit version of Vista, which is currently incompatible with our USB Cartridge Reader. Check your system to see if you are running Vista 32-bit or 64-bit by going to the Start Menu and selecting Control Panel -> System and Maintenance -> System. It should tell you there whether you have a 32-bit version of Vista or the 64-bit. If you have the 32-bit version, try plugging the USB Cartridge Reader into a different USB port, and allow Windows to automatically load the device drivers for it (the light in the memory cartridge should go out once they have been successfully installed).
If you have a 64-bit version of Vista, you can download via the cable you used for the telemetry. To confirm that the V300 is set up correctly for this type of download, select File -> Open Car Configuration, and open the config file you use to download. Once it is open, go back to File -> Show File Security Settings. Make sure that the recorder type says "V300S" for a serial cable download or "V300" if you are using the memory cartridge. If necessary, you can change this by selecting File -> Change File Security Setting and, selecting the proper type (V300S or V300).
Hopefully this helps. If you are still experiencing a problem, feel free to give us a call anytime at (949) 709-5555.
949-709-5555 ext. 1952