If it is a pure text file then you should be able to upload as .txt or as .html. If you tried to upload as .doc then it would fail as there would be a mismatch between the actual file type and the type stated in the extension.

Make sure the file really is ascii text. Give it a slightly different name and a valid extension then try again.

Remember that if you have free hosting you are limited in the file types that you can upload.