Few roots rotting, what to do?

[supersheep]

I've definitely got the Orchid bug! But I seem to keep on killing them! I'm hoping you can help with yet another ailing orchid!

I got one a fortnight ago and I repotted it the day I got it in fresh orchid compost. The roots looked very green and healthy.

Anyway, the last few days I've seen that a few of the roots near the base of the plastic pot are going a bit mouldy and black.

Is there anything I can do to help with this? The flowers are looking very nice still, but two of the small leaves near the base went yellow recently. The other 3 leaves look very big and green and healthy, as do the other roots.

So I think the orchid is still healthy enough, but I'm worried about the couple of roots that look like they're rotting...