WordNet (r) 3.0 (2006):

unreliability
    n 1: the trait of not being dependable or reliable [syn:
         undependability, undependableness, unreliability,
         unreliableness] [ant: dependability, dependableness,
         reliability, reliableness]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "unreliability":
   capriciousness, chanciness, changeableness, coquettishness,
   credibility gap, criticalness, danger, delicacy, desultoriness,
   deviability, doubtfulness, dubiousness, eccentricity, erraticism,
   faddishness, faddism, fickleness, flightiness, freakishness,
   frivolousness, hazard, hazardousness, implausibility,
   impulsiveness, inconceivability, inconsistency, inconstancy,
   incredibility, infirmity, insecurity, insolidity, instability,
   insubstantiality, irregularity, irresponsibility, levity,
   lightness, mercuriality, mercurialness, moodiness, peril,
   perilousness, precariousness, questionableness, restlessness, risk,
   riskiness, shakiness, shiftiness, shiftingness, skittishness,
   slipperiness, speculativeness, sword of Damocles,
   ticklish business, ticklishness, totteriness, touchiness,
   treacherousness, treachery, unauthenticity, unauthoritativeness,
   unbelievability, unbelievableness, uncertainty, undependability,
   unfaithworthiness, unfixedness, unhealthiness, unpredictability,
   unsafeness, unsettledness, unsolidity, unsoundness, unstableness,
   unsteadfastness, unsteadiness, unsubstantiality, unsureness,
   untenableness, untrustworthiness, variability, variation, variety,
   volatility, wantonness, waywardness, whimsicality