UPDATE: liveSite v7.3+ now supports being installed in a sub-directory. If you are still having this problem then please see this article.
You might have installed liveSite in a sub-directory (e.g. http://www.example.com/example/livesite/), which liveSite does not support. The software directory (e.g. livesite) must be placed in the web root (e.g. http://www.example.com/livesite/).