sip_xmit warning on asterisk 1.8.2.3

Asterisk Asterisk Support
1

Any idea why I keep getting these warnings??

[Jan 28 08:56:23] WARNING[23767] chan_sip.c: sip_xmit of 0x2aaab020cb60 (len 988) to 0.0.30.217:5060 returned -1: Invalid argument
[Jan 28 08:56:24] WARNING[23456] chan_sip.c: sip_xmit of 0x2aaab01f8210 (len 988) to 0.0.30.207:5060 returned -1: Invalid argument
[Jan 28 08:56:24] WARNING[23456] chan_sip.c: sip_xmit of 0x2aaab020cb60 (len 988) to 0.0.30.217:5060 returned -1: Invalid argument
[Jan 28 08:56:25] WARNING[23456] chan_sip.c: sip_xmit of 0x2aaab01f8210 (len 988) to 0.0.30.207:5060 returned -1: Invalid argument
[Jan 28 08:56:25] WARNING[23456] chan_sip.c: sip_xmit of 0x2aaab020cb60 (len 988) to 0.0.30.217:5060 returned -1: Invalid argument
[Jan 28 08:56:27] WARNING[23456] chan_sip.c: sip_xmit of 0x2aaab01f8210 (len 988) to 0.0.30.207:5060 returned -1: Invalid argument
[Jan 28 08:56:27] WARNING[23456] chan_sip.c: sip_xmit of 0x2aaab020cb60 (len 988) to 0.0.30.217:5060 returned -1: Invalid argument