Invalid Startline

Anyone know what this message means in the logs?  Having some issues with a customer and I see their IP appearing in the logs, but I'm not sure what it means.

Mar 27 17:54:49.321 atcpd02@4SBC3: MESSAGE[10] SipServiceSocket 5.6.7.8:5062 got invalid startline from 1.2.3.4:49245

Mar 27 17:54:49.321 atcpd02@4SBC3: MESSAGE[10]   0000: 52 65 66 65 72 72 65 64 2d 42 79 3a 20 3c 73 69   Referred-By: <si

Mar 27 17:54:49.321 atcpd02@4SBC3: MESSAGE[10]   0010: 70 3a 34 36 38 32 38 37 39 39 36 32 40 70 72 6f   p:4681234567@pro.abc

Mar 27 17:54:49.321 atcpd02@4SBC3: MESSAGE[10]   0030: 2e 63 6f 6d 3e

Thanks!