  The CMB maps obtained by observations always possess domains which have to be
masked due to severe uncertainties with respect to the genuine CMB signal.
Cosmological analyses ideally use full CMB maps in order to get e.g. the
angular power spectrum. There are attempts to reconstruct the masked regions at
least at low resolutions, i.e. at large angular scales, before a further
analysis follows. In this paper, the quality of the reconstruction is
investigated for the ILC (7yr) map as well as for 1000 CMB simulations of the
LambdaCDM concordance model. The latter allows an error estimation for the
reconstruction algorithm which reveals some drawbacks. The analysis points to
errors of the order of a significant fraction of the mean temperature
fluctuation of the CMB. The temperature 2-point correlation function C(theta)
is evaluated for different reconstructed sky maps which leads to the conclusion
that it is safest to compute it on the cut-sky.
