(Redmine) how to fix an error with custom fields?

Question

I have an error, when I'm trying to access to the custom fields page in the administration tab (Administration -> Custom Fields -> 500 error):

Internal error

An error occurred on the page you were trying to access.
If you continue to experience problems please contact your Redmine administrator for assistance.

If you are the Redmine administrator, check your log files for details about the error.

In the production.log I have the following error:

Started GET "/custom_fields" for ip at 2015-02-05 09:33:42 +0000
Processing by CustomFieldsController#index as HTML
  Current user: user (id=1)
Completed 500 Internal Server Error in 8.0ms

ActiveRecord::SubclassNotFound (The single-table inheritance mechanism failed to locate the subclass: 'Impasse::ExecutionCustomField'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite CustomField.inheritance_column to use another column for that information.):
  app/controllers/custom_fields_controller.rb:29:in `block (2 levels) in index'
  app/controllers/custom_fields_controller.rb:27:in `index'

I also have several plugins installed:

Redmine Agile plugin (Light version) Scrum and Agile project management plugin for redmine http://redminecrm.com RedmineCRM 1.3.5 Configure

Redmine Checklists plugin (Light version) This is a issue checklist plugin for Redmine http://redminecrm.com RedmineCRM 3.0.2 Configure

Redmine Tags Redmine issues and wiki pages tagging support https://github.com/redminecrm/redmine_tags/ Aleksey V Zapparov AKA "ixti" 2.0.1-dev Configure

Redmine Tweaks Wiki and content extensions http://github.com/alexandermeindl/redmine_tweaks AlphaNodes GmbH 0.4.9 Configure

Redmine Wiki Extensions plugin This is a Wiki Extensions plugin for Redmine http://www.r-labs.org/projects/r-labs/wiki/Wiki_Extensions_en Haruyuki Iida 0.6.4

Redmine Work Time plugin A plugin to view and update TimeEntry by each user http://www.r-labs.org/projects/worktime

And I checked all these plugins on the clean redmine installation and thay works correctly, without any conflicts. Redmine version - 2.6.0

How can I fix this problem?

Answer 1

After discussion we found out that plugin impasse left custom fields in DB. After the plugin was removed Redmine can not load these custom fields any more.

Solution: find incorrect records (custom fields are records!) in Db and destroy them manually.