A WikiTree ID could be rejected by http://www.wikitree.com/wiki/Special:MergePerson for two reasons.
First, it could be an invalid ID, e.g. an ID that does not exist. This could just be because of a typo. You'll see a message like this: "Sample-8 is an invalid WikiTree ID. Please check your Watchlist for the ID and try again."
Second, it could be a redirected ID. This happens when a merge has already been completed for the profile. That is, it can't be merged because it's already been merged. You'll see a message like this: "Sample-8 is a redirected user, which cannot be merged."
Lorna, I know this question of yours connects with something discussed by e-mail. In your specific case I think a merge was half-completed and something interrupted it. This might happen if there's a problem with the Internet connection or server, or it might happen if the server is working on multiple commands related to the same profiles at the same time. All this should be unusual since we have many failsafes in place, but various bugs or problems are possible.
If it's a half-completed merge, we will need to look closely at the specific situation to see what was completed and what was not.
