well... count me in on this if you can. I have the same issue... but haven't really spent any time to figure it out. Admittingly... I skimmed the manual and found it a little confusing to my high school education (2.7GPA)...
When you install Nebula it creates a folder in the C drive named "nebulatemprepository". Inside this folder there are several folders. 2 of them are named "Vectors" and "Programs" respectively. When you add a library usually you have "vectors" and "programs" which need to be dragged (or copied or installed) in the respective folders mentioned above.
And if it doesn't? And if you don't have a C drive? I am not trying to be difficult! I have been considering trying Nebula also. But the OP never indicated they were using Windows. I don't know if that's something you just guessed, or were informed of from another post of theirs.
Doesn't matter what your drive/drives are called. When installing Nebula first you will be asked where you want to install the VST so select your VST folder obviously. Next is the location of the Nebula support folder called NebulaTempRepository. You can install it anywhere, on your second drive if you want, as stated above the default is C:\NebulaTempRepository. If you want to install to a different drive, say drive E, you can change it to E:\NebulaTempRepository. Inside that folder are the Programs and Vectors folders, to install libs simply copy the Programs to the Programs folder and Vectors to the Vectors folder as stated above.