…you have a classic case of “nstreme is not compatible with 802.11n standard”… Search this forum… there are quite a few posts about this problem…
If you’re forced to use the “n” standard, try NV2 instead of nstreme…
edit:
Check this: http://forum.mikrotik.com/t/nstream-is-not-suitable-for-2x2/65604/1