This is a known problem that only occurs with the latest Sound Forge 9.0c update.
There is a simple solution and following these steps should resolve your problem:
1. Open Sound Forge, close any open files and remove any UAD plugins in use.
2. First, you can revert your sound device buffer sizes back to the previous settings.
If this isn't configured already, we do recommend that you always use ASIO with Sound Forge and the UAD plugins (Options>Preferences...>Audio... Your ASIO device must be selected for "Audio device type")
Now you need to change some "internal settings" in SF9 as a fix for your original problem:
1. Hold down Ctrl+Shift while selecting Options>Preferences...
2. Select the “Internal” tab
3. Type in “sfaudstrm” in the edit box at the bottom
4. Find the entry labeled “Default SfAudStrm read size”
5. Change the Value cells to:
Default SfAudStrm read size 131,072
Default SfAudStrm read cache 2,097,152
6. Tab or click away from the cells to commit the values, then click OK
7. Restart Sound Forge
UAD plugins should now process correctly in SF9c.
Sony has informed us that this problem will not occur again in future updates of Sound Forge which will maintain these compatible settings.