  We present two results which combined enable one to reliably detect
multimode, multipartite entanglement in the presence of measurement errors. The
first result leads to a method to compute the best (approximated) physical
covariance matrix given a measured non-physical one. The other result states
that a widely used entanglement condition is a consequence of negativity of
partial transposition. Our approach can quickly verify entanglement of
experimentally obtained multipartite states, which is demonstrated on several
realistic examples. Compared to existing detection schemes, ours is very simple
and efficient. In particular, it does not require any complicated
optimizations.
