Vista - dsound.dll error

I have had the following error for a few weeks and it is totally disabling my audio except for basic system sounds.

C:\Windows\system32\dsound.dll is either not designed to run on Windows or it contains an error. Try installing the program again using the original installation media or contact your system administrator or the software vendor for support.

I have tried deleting (as admin), renaming and replacing the file, updating the system, reinstalling DirectX and my soundblaster software to no avail. Vista will not let me delete or rename the file even in "DOS" mode. (yes, I am old school and can DOS)

I really, really miss playing BF2. Any options I have not thought about or anything else I can try? The MS website is useless on this matter (no earth shattering news there, huh?)

I have installed Vista x64 ultimate, Soundblaster Audigy 2 ZS card, 7.1 speakers.

Most applications with sound open up to that error message.

Thanks

That file is part of direct x, have you downloaded the august 2008 update if not here is the link.

Download details: DirectX Redist (August 2008)

Thanks for the reply.

I already tried that. I get messages that it's already up to date.

Any other suggestions?