Problem with nf_ct_sip module

Hello,
after installing and adding about 1500 accounts on the server I’ve got a lot of errors in console:

Message from [email protected] at Feb 3 14:48:35 …
kernel:nf_ct_sip: dropping packetIN=eth5 OUT= MAC=00:15:5d:0d:48:0d:f0:25:72:52:b3:c4:08:00 SRC=172.28.96.108 DST=194.105.144.215 LEN=695 TOS=0x00 PREC=0x00 TTL=248 ID=24111 PROTO=UDP SPT=5060 DPT=5060 LEN=675

Message from [email protected] at Feb 3 14:48:35 …
kernel:nf_ct_sip: dropping packetIN=eth5 OUT= MAC=00:15:5d:0d:48:0d:f0:25:72:52:b3:c4:08:00 SRC=172.28.96.108 DST=194.105.144.215 LEN=695 TOS=0x00 PREC=0x00 TTL=248 ID=24112 PROTO=UDP SPT=5060 DPT=5060 LEN=675

Message from [email protected] at Feb 3 14:48:36 …
kernel:nf_ct_sip: dropping packetIN=eth5 OUT= MAC=00:15:5d:0d:48:0d:f0:25:72:52:b3:c4:08:00 SRC=172.28.96.108 DST=194.105.144.215 LEN=695 TOS=0x00 PREC=0x00 TTL=248 ID=24113 PROTO=UDP SPT=5060 DPT=5060 LEN=675

Message from [email protected] at Feb 3 14:48:37 …
kernel:nf_ct_sip: dropping packetIN=eth5 OUT= MAC=00:15:5d:0d:48:0d:f0:25:72:52:b3:c4:08:00 SRC=192.168.32.150 DST=194.105.144.215 LEN=468 TOS=0x00 PREC=0x00 TTL=62 ID=0 DF PROTO=UDP SPT=5060 DPT=5060 LEN=448

these are only several errors from console.

Specified source IPs cant register on the server.
Messages comes each 1-2 seconds.

What temporary resolved issue is only reboot server. After 2-3 hours after reboot it occurs again.

Please help.