I've got a couple 333 boards running 3rc6 (it came on them) I programed them with my laptop a couple weeks ago and now when I try to Winbox in with my laptop it hangs downloading plugins, doesn't matter if I try it by IP or MAC, same response. I can Winbox into other gear just not any of the 333's I have running 3rc6. I've serialed into the one system reset and I deleted the mikrotik cache folder thinking maybe it was a bad previous plugin and still no joy. I even tried a new out of the box 333 and it done the same thing. I hooked up another laptop and I can Winbox in with it.

Suggestions on what else could be causing this?

when ive seen issues with direct connections to RB via winbox, its usually a sign of a too weak power supply, or a power supply that is failing / failed. (power supply to the router board that is).