This error message, on imports, indicates that you have blank rows in your import file. These are usually at the bottom. In Excel these blank rows and other blank rows that don't affect the imports are visually indistinguishable.
There is no easy way to determine if where these blank rows are, or even how many there are. The only way to do this would be to save your Excel sheet as a Comma Separated Value (CSV) file and open the file up in Notepad or other similar text editor. There will be some lines that are just a series of commas ( ,,,,,,,,,, ). Delete these rows and save.