I guess Forum2tech is right and most likely you have in your .csv file the columns with exactly the same names of headings. Please, check your file. If you do not need the information in that columns with duplicated headings, you can simply delete them.
In case you need those additional data in that columns with the same names, I can offer you an alternative solution - desktop application called Store Manager for Magento.
Using it you can choose from which column of your .csv file you would like to take information and where exactly (to which field of database) you would like to load the information.
For example, if you have 2 columns called Description, then using Store Manager you can assign one column with description to general product description and second column you can assign to short description.
In any case, if you are interested, here is free 2-weeks version of Store Manager available for download -