This is an issue with th:wiki:AccountManagerPlugin
Please fill in a ticket on trac-hacks.org, as this plugin is not (yet?) managed on this site.
You may want to ask for support on the MailingList first, as this issue might come from an invalid/incomplete installation (missing template file)
BTW, when you submit a ticket, please use verbatim blocks ({{{ }}}) for pasting Python traceback (use preview to check that it is displayed as expected), do not forget to specify which version of Trac you're using and be fair with the severity field.