500 Internal Server Error? Here's an obscure fix

I've found a number of threads related to the "500 Internal Server Error", but none of the solutions seemed to apply to this particular case. Since I didn't see this suggested anywhere else, I thought someone might find it useful.

One of my clients' websites was returning the dreaded error message after having added an .htaccess file to what he thought was the root of his website. In fact he had uploaded the .htaccess file into his home (ftp) directory. As soon as the .htaccess file was removed, the website was back to normal.

Admittedly, this is probably going to be a rare user error, but I hope somebody finds it useful.