As one of Vuo's developers, I work on Vuo's engine (the thing that makes compositions run), work on nodes, and write documentation. You'll see me on the forums answering people's questions about Vuo.
I've been developing apps and frameworks for several years (since I was in college). Pre-Vuo projects include Kineme Quartz Composer plugins, iOS apps for education, an app that analyzes photographs of tomato slices, and software to help people with disabilities use talking keyboards.
I enjoy using Vuo to make live music visuals. My hope for Vuo is that it will grow into a community of people of diverse backgrounds and identities making lots of different artistic, useful, unique, goofy, beautiful, crafty, wonderful compositions.
Yes, I think you're right about case-sensitivity being the issue. I'm glad you pointed that out, or it might have taken us a while to guess! The nodes that refer to the library (including Calculate, Calculate List, Make Parametric Grid Mesh, and Make Parametric Points) call it "muParser" when it should be "muparser".
Until we get this fixed, you may be able to work around the problem by renaming the library file:
Right-click on your Vuo Editor.app file and choose Show Package Contents.
Go to Contents > Frameworks > Vuo.framework > Versions > Current > Modules.
Rename libmuparser.a to libmuParser.a.
Go to Finder. (For example, click on your Desktop so that the menu bar says "Finder".)
Hold down the Option key and select Go > Library.
Go to Library > Caches > org.vuo.
Delete the folder whose name corresponds to your current version of Vuo (e.g. 1.2.6).
Restart Vuo Editor. (It will take longer than usual to start since it will need to rebuild the cache you just deleted.)
If you first made (Loyalist )ConvocationGUI.vuo as a regular top-level composition, the Fetch Image nodes would have worked fine because they were referencing image files relative to that composition file (like ../../../../Desktop/LC Convocation VUO Master/Image Elements/GUI_Buttons/Zoom Increase.png). If you then changed it to a subcomposition, (Loyalist )ConvocationGUI.vuo would have been moved to your User Modules folder, and it would then be looking for image files relative to the new location of the composition file — so it would no longer be able to find them.
As a workaround, you can edit the values of your Fetch Image nodes' URL input ports, making them absolute paths instead of relative to the (sub)composition file. For example, change ../../../../Desktop/LC Convocation VUO Master/Image Elements/GUI_Buttons/Zoom Increase.png to ~/Desktop/LC Convocation VUO Master/Image Elements/GUI_Buttons/Zoom Increase.png. (The ~ is an abbreviation for /Users/[your username].)
The cable from Render Scene to Window to Curve is putting extra events into your Process List loop, which can cause problems. You can fix it by inserting a Hold Value node, like in the attached composition.