When you are wanting the images in your slideshow to be in motion (up, down, left, or right), your images must be large enough to allow for that movement.
In other words, the images need to be larger than the space where you want them to be displayed, otherwise CrossSlide will not work.
If CrossSlide or your Cycle slideshow isn't working it's usually because it can't find the images you want to display. This can be because the file name has been mistyped, or if an image hasn't been added to the Page Assets (for RW4) or the Resources section (for RW5).
Another common reason is when the folder for a page has been renamed. In the RapidWeaver® Page Inspector, under the "General" tab, there is a field called "Folder" and one for "Filename". If you are using RapidWeaver® 4 changing the "Folder" field can change where Page Assets are stored.
A Quick Overview of Page Assets in RW4
By default a page's assets are stored in a folder called "assets", but when adding a forward slash to the Folder field in RapidWeaver®'s Page Inspector, the assets are instead stored in a folder called "pageFilename_assets" where pageFilename is the name of your page as seen in the Filename field. For example, if you've changed the Filename to pictures.html and changed the Folder to something like "/vacation", then the page assets for the pictures.html page will be in a folder called "pictures_assets".
You may also have noticed that the home page cannot have the Folder field renamed with a forward slash. However, when you rename the folder of other pages with just a forward slash "/", RapidWeaver® renames the assets folder for the index.html page to be "index_assets".
For example, if you're using CrossSlide in RW4, look at the code snippet and you'll notice that is looking for your page assets images in a folder called "assets" - if you've changed the Folder in the Page Inspector so that it includes a forward slash "/", just change this value to "pageFilename_assets" (without the quotes) and CrossSlide should work properly. Note that you need to make similar changes for each page where you've changed the folder name to include a forward slash.
For more information about "Page Assets" in RW4 and how they differ from "Resources" in RW5, see this post on the NimbleHost blog.