  We study the topological order in RVB state derived from Gutzwiller
projection of BCS-like mean field state. We propose to construct the
topological excitation on the projected RVB state through Gutzwiller projection
of mean field state with inserted $Z_{2}$ flux tube. We prove that all
projected RVB states derived from bipartite effective theories, no matter the
gauge structure in the mean field ansatz, are positive definite in the sense of
the Marshall sign rule, which provides a universal origin for the absence of
topological order in such RVB state.
