  We study the problem of communicating over a single-source single-terminal
network in the presence of an adversary that may jam a single link of the
network. If any one of the edges can be jammed, the capacity of such networks
is well understood and follows directly from the connection between the minimum
cut and maximum flow in single-source single- terminal networks. In this work
we consider networks in which some edges cannot be jammed, and show that
determining the network communication capacity is at least as hard as solving
the multiple-unicast network coding problem for the error-free case. The latter
problem is a long standing open problem.
