  We analyse the consequences of the recently measured parallax of SS Cygni
(Harrison et al. 1999) on the accretion disc limit cycle model. Using the
observed long term light curve of SS Cyg and d=166 pc, we obtain for the mean
mass transfer rate 4.2*10^(17)g/s. In addition, we calculate the vertical
structure of the accretion disc taking into account heating of the outer disc
by the stream impact. Comparing the mean accretion rate derived from the
observations with the calculated critical mass transfer rate, we find that the
disc instability model disagrees with the observed long term light curve of SS
Cyg as the mean mass transfer rate is greater or similar to the critical mass
transfer rate. The failure of the model indicated by this result can be
confirmed by considering that the accretion rate at the onset of the decline
should be exactly equal to the value critical for stability. In contrast to
this prediction of the model, we find that the accretion rate required to
explain the observed visual magnitude at the onset of the decline must be
significantly higher than the critical mass transfer rate. Our results strongly
suggest that either the usually assumed temperature dependence of the viscosity
parameter alpha is not a realistic description of the disc viscosity, that the
mass transfer rate in SS Cyg noticeably increases during the outbursts or,
finally, that the HST distance of 166 pc, is too high.
