Import from CSV going wrong!!!

I have imported a list of files as CSV file. I have the CSV Import window open and everything looks great.
However, when I Import to the rename window, some of the New Filenames change!? With some of them, the extension has changed, with some the entire name is different.
This is very frustrating as I have a list of 16,000 files that need renaming.

Please can someone help me ASAP as I'm on a tight deadline?

Thanks so much in advance.

You're doing something wrong!

That's the best answer you can expect unless you provide us with sufficient information about what you need to do and how you are trying to achieve it.