  The puzzling correlation between the spin parameter lambda of galactic disks
and the disk-to-halo mass fraction fdisk is investigated. We show that such a
correlation arises naturally from uncertainties in determining the virial
masses of dark matter halos. This result leads to the conclusion that the halo
properties derived from fits to observed rotation curves are still very
uncertain which might explain part of the disagreements between cosmological
models and observations. We analyse lambda and fdisk as function of the adopted
halo virial mass. Reasonable halo concentrations require fdisk=0.01-0.07 which
is significantly smaller than the universal baryon fraction. Most of the
available gas either never settled into the galactic disks or was ejected
subsequently. In both cases it is not very surprising that the specific angular
momentum distribution of galactic disks does not agree with the cosmological
predictions which neglect these effects.
