aperture library could not be opened because the file system of the library's volume is unsupported.

Move the Library to a volume formatted Mac OS Extended (Journaled)

Regards

TD

how do you move the library

Is it Managed or Referenced?

See this page to format your drive: Format external drives to Mac OS Extended before using with Aperture

After your external drive is formatted correctly, drag the Aperture library to the drive. Formatting will erase the drive. SO besure to backup any files to a different volume before you format your drive.