Working with libraries

I'm struggling a bit getting up and running. My goal is to try to get a very simple language integrated into an existing project. Currently, we develop a series of libraries that others use to build a product. To build, they have to write some Java code. We are hoping that we can define a DSL that will make it much easier.

So I have created a simple language. The output of the language is a series of classes that all inherit from a root class that is defined in a Java class that is in a JAR. Based on my understanding, to use this language, I'm to create a new Solution, which I did, and placed the JAR file within that Solution, and defined it as a Dependency in the Solution Properties dialog. This is all done, and appears to be working fine. I am able to build the sandbox project and I can see the correct .class files that are being outputted.

Now, I'd like to build a plugin for IDEA. So I follow the instructions (https://confluence.jetbrains.com/display/MPSD34/Building+IntelliJ+IDEA+language+plugins). Everything appears fine, but when I build, I get an error, 'cannot find 'platform.jar' in local layout (platform.jar is the dependent JAR). 

Does this mean I have to copy this JAR to the build Solution as well? Are there any steps above that I'm doing incorrectly that may be causing this? I'm really trying to do this the 'right' way, but the documentation is very confusing when it comes to using external libraries.