The ability to reply from HTML emails is highly dependent on small details such as what browser, email client, operating system, and Internet provider you are using. Because everyone's system configuration is different, LiveJournal does not guarantee this ability. Small changes to any one of a number of system configuration details, some of which users have no control over (such as settings at your Internet Service Provider) can cause this ability to stop working.
Here are two things that you can do that may possibly get it working again.
- Make sure that your web browser is defined as your default browser, both by your system and by your email client. Make sure the browser is running and you are logged into LiveJournal when you are attempting to reply. You do not need to be at the LiveJournal site when you type your reply in email.
- When replying to the comment email, don't type your reply in the "preview" pane of your email client. Click or double-click on the email to open it in a new window, and type your reply there.
Also, please note that many popular email providers such as AOL and Hotmail "mangle" portions of HTML email, which can cause HTML mail to display improperly and the ability to comment from HTML email to stop working. Some symptoms of this include improper links, buttons that fail to lead to pages on the LiveJournal site, error messages such as "invalid password" or "could not determine journal from arguments", etc. LiveJournal has no control over this, as it is a function of the HTML cleaner used by these email providers.
If none of this information helps to resolve the problem, you will need to reply to the comment using the LiveJournal Web Interface. Each comment email you receive includes a number of links, and clicking on the "Reply at the web page" link will take you directly to the Reply page for that comment.