They had to estimate the last few days of December '05 based on an average of all the days in the month as they had a problem at the end of the month. Therefor, if you made more in the last few days your check was underestimated and extra amounts added to the check just received for January. If you earned way less than your average in the last few days of December, then they probably sent you too big of a check for December and deducted the excess from the January payment you just received. This could or could not be the reason for this issue of yours. I would call them and ask them directly. Good luck.