Did you ping the websites nicehash and westhash? Which is closer to you? Use the closer one and try again. Try decreasing the difficulty again or with no difficulty parameter.
-MZ
I'm on the west coast of the US so I assume westhash is closer and that's my primary with nicehash as a failover. The ping times are quite similar though.
I set difficulty to 8192 and I'm going to let that run until I check it later tomorrow. I already tried with no diff and that produced 330 MH/s effective hashrate and 5.2% reject rate after 24 hours. That might be the best I get if I stayed at westhash.