  The observed energy spectrum of ultra high energy cosmic rays (UHECR) is
distorted by errors in the energy reconstruction. Here we show that if the
shape of the error distribution is lognormal, the high end of the cosmic ray
spectrum will be distorted. This is distinct and potentially more significant
than the effect of the magnitude of the error in the energy. We estimate the
UHECR spectrum at the Earth assuming it is originated from a cosmological flux.
We then convolute this flux assuming a lognormal error in the energy. We show
that if the standard deviation of the lognormal error distribution is equal or
larger than 0.25, both the shape and the normalization of the measured energy
spectra will be modified significantly. As a consequence the GZK cutoff might
be sufficiently smeared and as not to be seen. This result is independent of
the power law of the cosmological flux. As a conclusion we show that in order
to establish the presence or not of the GZK feature, not only more data is
needed but also that the shape of the energy error distribution has to be known
well.
