I am trying to use Pianissimo as a plugin, but I keep getting this error: "Error Loading Sample Data."

Pianissimo currently requires a contiguous block of 250 megabytes of RAM in order to load its sounds. Try to arrange it so that Pianissimo is the first plugin that loads in your project. This problem generally only happens with existing projects. So, with an existing project, try removing the other plugins in the project, then loading Pianissimo and then reloading the rest of the plugins.