Missing Cells
 

I created a workbook in Excel 2003, and entered various data. Some of the
data was typed in, and then some whas copied from other workbooks. I then
proceeded to have the columns auto filtered. Now when i use this feature, i
am not able to auto filter to some cells? The only one that are of importance
are the one containing Text (which are formated that way). Does anyone know
why this is?