Secure RTP problem

Hi guys,
[Sep 20 14:48:33] WARNING[4503][C-00000025]: chan_sip.c:10474 process_sdp: Matched device setup to use SRTP, but request was not!
What can i do ?

[400]
type=peer
secret=123456
host=dynamic
context=phones
dtmfmode=rfc2833
disallow=all
allow=g722
transport=tls
encryption=yes

[phones]

exten => 100,1,NoOp(First Line)
exten => 100,n,NoOp(Second Line)
exten => 100,n,Dial(SIP/100)
exten => 100,n,Hangup

exten => 200,1,NoOp(First Line)
exten => 200,n,NoOp(Second Line)
exten => 200,n,Dial(SIP/200)
exten => 200,n,Hangup

exten => 300,1,NoOp(First Line)
exten => 300,n,NoOp(Second Line)
exten => 300,n,Dial(SIP/300)
exten => 300,n,Hangup

exten => 400,1,NoOp(First Line)
exten => 400,n,NoOp(Second Line)
exten => 400,n,Dial(SIP/400)
exten => 400,n,Hangup

Set encryption=no, or do whatever you need to do on the device that is equivalent to setting encryption=yes.