If you really do mean 3 LETTER .biz (LLL.biz) and not 3 character .biz (LNL.biz , #LL.biz , etc.), then register.
I just scanned the first 10,000 and didn't find any available (Still 7,000 left to check, of course), so my gut says that your software might be having issues...
However, if it's located further down the line: register that bad-boy, :imho:
-Allan :gl: