How to reproduce:
Install RhodeCode 1.2.0 beta
Login as an Administrator (built-in account created during the install process)
Select the username link leading to /_admin/my_account/
An excption is raised
Note that this does not happen to administrator user accounts created by the user interface in the application. Apparently only the built-in account is affected. Also, the built-in user can in fact edit his own user through the user edit interface (/_admin/users), just as he can edit any other user.
I'll include a full stack trace of this exception here as soon as I can.