First off, we need logs, can't do anything without logs, secondly, you need to make sure to have "installed" the server instance. Simply start up the installer, tell it to "install" in the same directory that your installer is in, after that upload the libraries, Minecraft server jar and the Cauldron jar itself. Try to start up the server and look for the jar its looking for in the console and rename the Cauldron jar to the server jar they're looking for. This should fix your problem for the most part, but as Slind said, there's an issue with Mystcraft to IC2 compatibility right now that makes it impossible to start up a server on Cauldron with Mystcraft enabled. Unless of course, you want to disable IC2 rubber trees.