The usual cause of this error is if your connection has been interrupted during a previous session.
You can fix this problem by using FTP to connect to your site. Then, delete the 'service.lck' file from your public_html/_vti_pvt directory.
You may receive more errors after you solve this problem this way. If that is the case, simply uninstall/reinstall the Front Page extensions from your Cpanel. All should return to it's normal wellness status after that. :)