I know they have recently changed their mining site, it may have something to do with that.

Also, be sure that you are using the correct difficulty for your rig

Available ports:

    3350 - Vardiff 16 - 131072
    3351 - Diff 1024
    3352 - Diff 4096
    3353 - Diff 16384
    3354 - Diff 32768
    3355 - Diff 65536
    3356 - Diff 131072
    3357 - Diff 262144
    3358 - Diff 524288
    3359 - Diff 1048576


http://coincave.nl/popstats.php