For some odd reason, that I'm sure makes sense to whoever coded the site, you cannot view any chapter but the most recent if you aren't logged in to the site. Even worse, there's no way to find this out until you are already logged in and can finally access earlier chapters.
On any rational site they would include that fact both on the chapter list page and in the banner that pops up explaining the benefits of logging in but instead they just talk about things like bookmarks... At the very least you would think there would be a stickied thread about it somewhere in the support forum, but no, that would be too simple and wouldn't allow the site to punish people who dare to want to read manga anonymously.
Even worse, if you try to follow a link to an earlier chapter (by selecting it in the chapter drop down list once you are viewing the most recent chapter) it just gives a 404 not found error which would usually mean the page has been deleted/moved/corrupted/etc. from the server.
This is, needless to say, a pain in the ass for new users and makes it appear that this site is missing/lost/removed a shit ton of content compared to the many other free manga viewer sites available.
So obviously, my suggestion is to fix this. Preferably the site would stop requiring you to create an account to view manga like every other manga site out there.
If, for some reason, that's not possible I would suggest adding a note on the homepage and chapter lists explaining that you can only view the most recent chapters if not logged in and instead of a standard 404 error page redirect such users to a login page indicating that viewing the page requires the user to be logged in (like any other site does when trying to follow a link to a page that can only be viewed when logged in)