Speed is not officially supported in Pro Tools 10, though there are many who use it without error on that platform. If you are using Speed in Pro Tools 10 and experience an issue where Speed outputs silence (rather than processed audio), here is one potential solution, though we cannot guarantee this will work for you.
Open up the Preferences menu, select the "Processing Tab," and set the Default Handle Length to 0.00 seconds, rather than 2.00 seconds, you might have better luck. Another thing you can try, if the audio processing is still not working properly, is to change the sample rate to something else and try again. However, we do not guarantee support in PT10 at this time.