Asterisk not sending 200 OK to TLS enable peer

I am keep getting this error always.
Asterisk after receiving 200 OK from one peer is not sending 200 OK to TLS enabled peer.And log shows below warnings.
<— Reliably Transmitting (no NAT) to x.x.x.x:5061 —>
SIP/2.0 200 OK

WARNING[26581][C-00000012]: chan_sip.c:3990 __sip_xmit: sip_xmit of 0x852f868 (len 444) to x.x.x.x:5061 returned -2: Resource temporarily unavailable

What does this mean.