Maybe SmartSound is no longer available for PR. At least their website makes no mention of it still being available. Sonic Fire Pro is still available however.
There was an initial problem with the SmartSound plug-in and the early releases of CS4. Both Adobe and SmartSound were working on this, each from their own end.
It was my understanding that with CS4.1 and the latest SmartSound plug-in, things were "fixed." If you have the latest version of each and it's still not working, then my understanding is wrong. I had corresponded with SmartSound TS, some time back, and they indicated that the fix was close. If it does not work yet, I'd contact SmartSound TS and inquire. They are very nice folk and should give you a target date, plus the new version #.
As Harm mentions, SonicFire Pro will do much more than the SmartSound plug-in, however it is a stand-alone program. The basic version is free with the purchase of any of the Strata Series media. The full-version is a free upgrade from SonicFire Pro 4/4.5 to the new, and improved 5. The drawback is that one will need to do a "reference Export" to effectively score the production in SonicFire Pro. I hold out hope that it can one day be a plug-in, but I do not see that happening anytime soon. SmartSound TS was very closed-mouth on that, so I do not expect to see anything until at least SonicFire Pro 6 and CS5, if then.
Good luck, and please report what SmartSound TS has to say.
If you left CS3 installed, just go back to it with a new dummy project and create a sound clip of the required length as I have been doing.
But if you come up with anything new from Smart Sound please let us know.