This problem is also due to date time format and text format. If you convert the column of all the rows to datetime value or text value. this problem will be solved. This problem occurs due to in some records the date is internally in datetime format whereas in some rows it is either general or text.
To Convert All the values to date please follow these steps
Highlight the cells (only one column wide) containing the dates. You can select the entire column if you like.
From the Data menu, select 'Text to columns'
In the dialog box, select the 'Fixed width' option and click the Next button
If there are any column break lines (vertical lines with arrows) through the data area, double-click on them to remove them all. Then click the Next
In the 'Column data format' section, select MDY (or whichever date format you need) from the Date dropdown. This tells Excel the format of the imported dates.
Click the Finish button.