issue when running the sample SpeechToText _WPF_sample

[watorkhani]

Hi,
When we try running the sample SpeechToText_WPF_sample (with a free subscriptionKey), somtimes it works but frequently we are blocked with :
--- Start speech recognition using microphone with ShortPhrase mode in en-US language ----
--- Microphone status change received by OnMicrophoneStatus() ---
********* Microphone status: True *********
Please start speaking.

and after a few minutes (maybe 1 or 2 minutes) we get this message (and all radiobutton are disabled) :
--- Microphone status change received by OnMicrophoneStatus() ---
********* Microphone status: False *********

i don't think its a network problem because when i test with a bad SubscriptionKey i get instantely this error message :
--- Error received by OnConversationErrorHandler() ---
Error code: LoginFailed
Error text: Transport error

could you help us please ?

Regards,
Wajdi