Why won't my converted excel to CSV file download into my QBSE ?

What was "converted" that you're trying to Import?  And do you know if it is truly in a format that QBs will accept?  I don't mean just a .CSV file.  But what is it you're trying to import and are the columns, headers, etc. set up to correctly so QBs will recognize the Data you're trying to Import? 

Give us a little more info and maybe someone here will know the answer.