https showing blank pages

When I surf to a site on my server that doesn’t have ssl, for example:
after all the warnings & accepting of certificates, I get a page that reads:

Index of / [ICO] Name Last modified Size Description

Nothing else. Surfing to other parts of the site that are normally there return a 404.

I imagine some people might stumble on the https version of one of these sites and become frustrated, especially after cookies keep them coming back to the https version.

By the way: I have one SSL site on its own IP. Several non-SSL sites share an IP. Is there a way to disable https access for the sites on the shared ip?