A couple of weeks ago, a security exploit was found in the slideshow plugin. To prevent XSS attacks, I closed off any HTML until a solution was available. This was version 2.1.15.
If you're running 2.1.16 or 2.1.17 now, HTML should work, though in a strict and limited way. On my site you can read about the allowed tags and its attributes.
Perhaps the only thing you have to do is rewrite and save the HTML since it may currently be in a broken format.
Otherwise you could perhaps paste your HTML here, and I'll have a look at it for you.