first reboot the machine and try again And while you are restarting hold down the Shift key for safe Boot mode. If that fails doulbe click on the Library itself and see if that starts Aperture. Write back an tell us what you found out
The Library would of been created the first time you opened Aperture.... So Im hoping you had an earlier version with a created Lib.
Try running disk utilites and repairing permissions.
Try holding the Command + option key while clicking on the Aperture icon to repair its permissions specifically
When I mentioned click on library itself I should of said locate the Aperture Library (pictures folder?) and double click on that to start aperture. Also to open a lib hold the option key and click on the Aperture icon. A dialog should appear to choose the library. Write back and tell us specfically what you did. we need to know what you performed so we can eliminate options. good luck