Redmine

Hi all,

I have an error from redmine 3.3.1 with custom fields.
Thing is I have several custom fields which I created for my project. I have reorganized my category lists and figured out I don't need those custom fields anymore
So I have removed all issues out of these custom lists, I checked again by filter all issue which related to
Now I want to delete those custom fields but my redmine said "Unable to delete custom fields", I checked logs but no error expected

Anyone please help!

Below is my redmine environment:

Environment:
  Redmine version                3.3.1.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-darwin16]
  Rails version                  4.2.7.1
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.9.4
  Git                            2.9.3