The Collaborative International Dictionary of English v.0.48:

Inaccessibility \In`ac*cess`i*bil"i*ty\, n. [Cf. F.
   inaccessibilit['e].]
   The quality or state of being inaccessible; inaccessibleness.
   "The inaccessibility of the precipice." --Bp. Butler.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inaccessibility
    n 1: the quality of not being available when needed [syn:
         inaccessibility, unavailability] [ant: accessibility,
         availability, availableness, handiness]