Issue Re-Opening FCPX Libraries from External HD

Hey everybody,

When finished with a FCPx project, I started to click on the library and select "Reveal in Finder" such that I could copy the entire library over to a wireless external hard drive. I would then delete the library off my MCP in order to save space. Now I'm trying to reopen the libraries that I had copied and am getting the following error:

"The document could not be opened. Please use a local or SAN location"

What does this mean? How can I reopen my library with all of my saved media inside?