I gained weight

yesterday & I don't know why. Makes me mad. I had a good day, I did have buttered popcorn for dinner. I know its not healthy, but I did stay within my
calories.
Start Weight -----310.00
Pounds To Lose ---110-150
-------------DAYS ON-------TODAYS---------TOTAL WEIGHT
---------------
DIET---------WEIGHT--------------LOST
01/14/08-------13-----------293.25---------------16.75
01/15/08-------14-----------293.75---------------16.25
01/16/08-------15-----------293.75---------------16.25
01/17/08-------16-----------290.75---------------19.25
01/18/08-------17-----------290.25---------------19.75
01/19/08-------18-----------289.50---------------20.25
01/20/08-------19-----------289.25---------------20.50
01/21/08-------20-----------287.75---------------22.25
01/22/08-------21-----------289.00

------------21.00
EXERCISE
--------------------------------------------------------DAYS
----------------------------------------TOTAL---------I HAVE
----------------------------------------MILES--------EXERCISED
--------------TODAY'S------------------THIS-----------THIS
---------------MILES----TIME----------MONTH---------MONTH
01/14/08-------0:00-----00:00----------13.25------------11
01/15/08-------1:27-----24:37----------14.50------------12
01/16/08-------1.36-----23:34----------15.85------------13
01/17/08-------0:00-----00:00----------15.85------------13
01/18/08-------1.39-----27:39----------17.20------------14
01/19/08-------0:00-----00:00----------17.20------------14
01/20/08-------1.40-----25:29----------18.60------------15
01/21/08-------2.10-----39:50----------20.70------------16
01/21/08-------0.00-----00:00----------20.70------------16