Thanks for reporting this. This is caused by trying to insert from a
file with data that is not UTF-8 encoded. I have file an issue:
http://code.google.com/p/forceworkbench/issues/detail?id=578
However, you should be able to workaround this pretty easily by re-
saving your file with UTF-8 encoding. This will depend on way you
created your CSV, but most applications will give you can option to
choose the encoding when you save. You can also use an application
like Notepad++ or TextWrangler to convert between character encodings.