After installation, error in expenses table

[reyezstef]

I get this error when I try to access /expenses, after installation of your plugin. Before installing it seemed to work fine.

Processing by ExpensesController#index as HTML
  Current user: me (id=28)
Completed 500 Internal Server Error in 7ms (ActiveRecord: 0.5ms)

NoMethodError (undefined method `sum_by_period' for #<Class:0x000000092d6410>):
  lib/redmine/sudo_mode.rb:63:in `sudo_mode'

[wesley-jones]

Hey reyezstef, it sounds like you have another plugin installed that is already using the URL /expenses. This will conflict with the contracts plugin. Do you know what plugin was already using that URL?