conditional formatting and blank cells

im comparing two different columns. One colomn is a manual input (me putting in scores) the column being compared is what the actual score is. Im trying to right a simple format if cell a1 does not equal cell b1 highlight red, if they are equal, no highlight.
problem is there are spaces between the rows as i work down the sheet, and the conditional formatting is highlighting these blank cells red even though there is no value in the cell. i used the same format in excel 2007 w/ no problems. any idea why excel is highlighting these blank cells???

thanks in advance.