Some DTMF missed in an IVR

I have a simple IVR(Automatic Attendant) that plays some voice and waits for user to enter his/her desired extension on DAHDI channel. While the user enters the digits on his phone some of digits are missed and IVR can not route the call to the right extension.
What is the problem?

IVR is as below:

include = default
exten = s,1,NoOp(VoiceMenu)
exten = s,n,Answer()
exten = s,n,Wait(1)
exten = s,n,Set(TIMEOUT(digit)=10)
exten = s,n,Set(TIMEOUT(response)=10)
exten = s,n,Background(intro)
exten = s,n,Playback(beep)
exten = s,n,WaitExten(10)

exten = _ZXX,1,NoOp(Dialing Extension)
exten = _ZXX,n,Dial(SIP/${EXTEN},20)
exten = _ZXX,n,Goto(VoiceMenu,bye,1)

exten = 0,1,Dial(SIP/100,20)
exten = 0,n,Goto(VoiceMenu,bye,1)

exten = t,1,Dial(SIP/100,20)
exten = t,n,Goto(VoiceMenu,bye,1)

exten = i,1,Playback(operation-not-valid)
exten = i,n,Goto(VoiceMenu,s,1)

exten = bye,1,Playback(operator-not-avail)
exten = bye,n,Playback(thanks)
exten = bye,n,Hangup[/code]

On the limited information available, people start keying the extenions during the beep.

Please use Asterisk Support, for support questions, in future.

Combine two lines into one and check.
exten = s,n,Background(intro)
exten = s,n,Playback(beep)

exten = s,n,Background(intro&beep)

–Satish Barot
Ahmedabad, India