I have a sub-script that runs under Vegas 8.0 but fails under 8.1

The sub-script requires access to the data in a WAV file and uses:
Microsoft.DirectX.DirectSound.dll

I know 8.1 and the Vista OS are 64bit, but the script is compiled as Win32 and runs most of the sub-scripts, except when starting the code block that accesses the WAV files.

I get the following error when starting the FindClicks script:
Could not load file or assembly "Microsoft.DirectX.DirectSound"
Version=1.0.2902.0,Culture=neutral,
PublicKeyToken=31bf3856ad364e35 or one of its dependancies.
The system cannot find the file specified.

Any ideas what could be going on?

Dennis