FL ID,S

Question. Got me fl id changer going again. Put most of my char id,s back in the changer except one. Entering the id with the one i have written down and when i hit create. It replies it can,t be found or if a mistake re enter it which i keep doing but same thing. I type exactly as written and the same id has been entered in the past when needed and no problem. Your advice please op. Appreciated