System.Speech.Recognition: SpeechRecognizer uses SAPI, so if you do not have SAPI installed by default (i.e. you are running XP), you need to install it. You do not need the entire SAPI developer kit, just redistributables (SpeechSDK51MSM.exe).
XP, SAPI 5.1; .
System.Speech.Recognition: SpeechRecognizer SAPI 5.1; SAPI 5.3; , .