It's not blocked by WSE, it's just programmed like shit and doesn't support the DirectX "version" we use.
You can "fix" it by opening My Documents\Mount&Blade Warband\crpg_beta_config.ini and changing
bUseDirect3D9ExIfAvailable=true
to
bUseDirect3D9ExIfAvailable=false
However if you turn it off you will experience increased memory usage and much slower alt-tabbing (comparable to pre-WSE2 Warband).