Try the following steps until the issue is resolved:

1. Open the import file
2. Modify the file path to the photos to end in the appropriate extension (i.e., .jpg, .gif, .bmp)
3. Save the file
4. Reimport

1. Open the import file
2. Modify the file path to the photos to ensure the correct path is selected and nothing is omitted
3. Save the file
4. Reimport

1. Open the import file
2. Remove any extra columns, leaving only the required columns.
3. Save the file.
4. Reimport

1. Save the import file to the Desktop
2. Reimport

NOTE: The import file must have CR or CRLF line endings.  This references the line breaks which occur after a line of text.  Reference en.wikipedia.org/wiki/Newline if this issue arrives during Importing