We reconsider the Casimir problem for the massless conformal scalar field in a 'half Einstein universe'. We first calculate the renormalized vacuum energy by using the mode sum method. Next, we calculate the renormalized vacuum energy-momentum tensor by using the point-splitting method. We construct the Green function by using the eigenfunctions, which are obtained by solving the wave equation with the appropriate boundary conditions. We discuss the importance of this case as well as its relation to previous calculations.