There are one and two letter domain names out there in nearly every extension. Most now are controlled by ICANN and other domain governing bodies.
Any one or two letter that is dropped, deleted, or expires goes to ICANN's coffers. It was reported that these would never be put into circulation again.
This is a story that I came across years ago regarding domain names and from a source that I am totally at a blank to recall. Never thought it would come up.
If this is a legitimate one letter domain, it is (or should be) privately held.
The "minimum length error" is the standard seeing the ICANN no longer permits the registering of a one or two letter domain name.
That is why the only way to buy one is from sellers like you and me...mainly you guys and gals.
I know other country codes (ccTLD's) were releasing them but I am not sure under what pretense.
There has been talk, and rumors, that there may be an auction by the euRID of the one and two letter .eu's. This may have been met with great fanfare a year or so ago but I think for the most part .eu has been a monumental flop in light of all the hype behind.