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Years ago I registered with bugtracker ( bugs.limesurvey.org ). Now, I want to log in to report a bug, and it does not work anymore. But I do not see a way to get a new password or reactivate my account, but I also cannot register anew because my alias and the mail-addresse are used. What can I do?

You need to contact the support.

Usually the password is the same as for the forum. The different accounts on Limesurvey (Manual-wiki, forum, Limesurvey account, translation, bugtracker) are all synchronized.

However, if this doesn't work, listen du Jelo: contact support. Open a support ticket, don't let them redirect you to the forum. We can't do anything about your password.