  We present a necessary condition for brane solutions to have their origins in
string field theory. For such solutions, T-duality operations between IIA and
IIB solutions should be well-defined. Nevertheless, not all S-brane solutions
have T-duality. The solutions that have T-duality and may accordingly be
regarded as low-energy solutions of string field theory satisfy a condition in
which some S-brane distributions are forbidden.
