After executed the product csv file of the Magento you may seen this CSV Import SKU error.So the reason is your csv format is
not in UTF-8 mode .This is the main reason generally this error comes when you are preparing CSV in microsoft office . I would suggest to use open office and manage your csv in UTF-8 mode.

How to change Encoding format

1-Click on the save button.Then give the file name.
2-Click file type as “CSV (Comma delimited)“.
3-Click on the Tools -> Web Options

4-Under the Encoding tab, select “Save this document as” drop-down box.
5-Select “Unicode UTF-8” format and click OK and Save button.

That’s all.