TYPO3 Core

When trying to upload and install extension "newloginbox" I get the error message:
Wrong file format. No data recognized, Error: MD5 mismatch. Maybe the extension file was downloaded and saved as a text file by the browser and thereby corrupted!? (Always select "All" filetype when saving extensions)

The file has been downloaded twice and does not appear to be corrupt. Others have had the same problem with various extensions. See bug 0004725. Also see http://lists.typo3.org/pipermail/typo3-dev/2004-September/006035.html

(issue imported from #M4826)