Usb error with Traktor S2 MK2 connected

Hello guys i have a big problem like many users of traktor s2 or s4 mk2.After a little use the controller stops responding.It is like i disconect it and the audio output changes to traktor form s2 to built in.In console it gives me this error : NIHardwareAgent: IOHIDDeviceRegisterInputReportCallback called with a null context Does anyone of you experienced something like this?What this erroe means?The problem is my mac or the usb device?I don't know what to do please help.Macbook Pro 2009 4gb ram 2,66 intel cpu.It's in great condition and never had a problem.I use lion 10.7.5 and traktor 2.6.8