Sounds like the user exists but doesn't show up in your list of users (or you didn't see him/her). Check again to make sure it isn't there already.
If not, make a check on the database integrety (there is an option for that) and see what happens.
If it is really a bug ti might have been solved long ago, because your installation hasn't been updated for almost a year. So before creating a bug report, update to the latest version and then see if the problem still exists.
Help us to help you!
Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.
