Phew, thank you very much.

What do you think why it caused problem?
I would like to use the component, can I try install it?
Or do you know any other problem ?

like you said...There was probably a problem with write permissions and the files couldn't be removed during uninstallation.

When I installed it, it wasn't success, why that happen?

many thanks.

Noriko

You said that you encountered the 500 error after installation, that means some problem with .htaccess file. Usually this is caused either by DirectoryIndex or Options FollowSymlinks lines.

I see...when this happened first, I deleted .htaccess.txt.

Now my site start working again, so I uploaded the .htaccess.txt and tried to install the JoomSEF again, but it couldn't work and 500 server error again. So I needed to delete .htaccess.txt again, then after login the admin, I uploaded it again...

Then now, I can see two Component of JoomSEF, how can I delete (uninstall) that?
I deleted some folder and data I new, but the components are still there.

And ...if possible I would like to use and test the component.
I don't know how to set up .htaccess.txt , would you instruct me for that?

Many thanks.

You need to manually remove the component from database in table #__extensions (replace #__ with your database tables prefix).

The .htaccess file must not have the .txt extension, it's just .htaccess. If you don't see such file on your server, some FTP clients don't display it because they treat it as hidden.

After installation if you encounter 500 error, open the .htaccess file and try to remove the DirectoryIndex line or the Options FollowSymlinks line.

There is no line of "DirectoryIndex" line or the Options "FollowSymlinks" line on my .htaccess file. what to do next?

Try commenting or uncommenting the line with RewriteBase. If that also doesn't help, check with your hosting company that the mod_rewrite is installed on your server and that the .htaccess file is enabled.