Thank you for asking this question in the support community forum. The "2015.01.14 15:54:04 SIP.STACK ERROR MSGBUILDER SIP Pre-Parser Error (UDP)" message is typically due to phones sending keepalive messages with invalid headers. When logged into the unit, to prevent this message from scrolling you can issue the no events command. This will stop these messages from scrolling, but it is on a per session basis.
I hope this makes sense, but please do not hesitate to reply to this post with any additional questions or information. I will be happy to help in any way I can.