Change your secondary DNS to match your primary. No need for it to point to an external because if you're offline it's moot.

Also, I would suggest using BFGMiner as a proxy instead of slush's. I've seen slush's have issues which couldn't be explained, but BFGMiner is always spot-on.

If possible, use a port other than 8332 to rule out port issues. I usually suggest folks use 8339 or something else easy to remember. Make sure the change is in blade setup, and the proxy knows to listen on the same port.