I've had similiar occurances. Once it was telling me that every good name I typed was available and I nearly jumped for joy. Seems to be an error in their look up system. Looks like it is indeed taken.
It could also mean that the domain is put for auction at their site and this is what it says "Use a Domain Buy Agent to get this name"
some script flaws happen everywhere.. go to domaintyper.com and search for "digit" dun b too happy if digit.com is available :)