Remapping key to <Nop> not working

Question

I'm trying to remap my Backspace key to do nothing in insert mode (want to start using more x and other different ways that are better for deletion in vim)

I added in my .vimrc this line:

inoremap <BS> <Nop>

But after restarting my vim the backspace still deletes a character.

What am I doing wrong?

This is part of my .vimrc:

set nocompatible
execute pathogen#infect()
syntax on
filetype plugin indent on
set laststatus=2
set background=dark
set number
set tabstop=4 softtabstop=0 expandtab shiftwidth=4 smarttab
set autochdir

set noswapfile
set backspace=indent,eol,start
set incsearch
set ignorecase
set fileencoding=utf-8
set encoding=utf-8
set gdefault
set smartcase
set scrolloff=5
let mapleader=","
map <C-n> :NERDTreeToggle<CR>

let g:ag_working_path_mode="ar"

let g:airline#extensions#tabline#enabled = 1
let g:airline#extensions#tabline#fnamemod = ':t'

let g:ctrlp_map = '<c-p>'
let g:ctrlp_cmd = 'CtrlP'

 set wildignore+=*/tmp/*,*.so,*.swp,*.zip
let g:ctrlp_user_command = 'find %s -type f'

set hidden
nmap <leader>T :enew<cr>
nmap <leader>l :bnext<cr>
nmap <leader>h :bprev<cr>
nmap <leader>bq :bp <BAR> bd #<CR>
nmap <leader>bl :ls<CR>

nnoremap <leader>w :w<cr>
nnoremap <leader>q :q<cr>

noremap > >><cr>
noremap < <<<cr>

let g:ctrlp_custom_ignore = {
            \ 'dir':  '\v[\/]\.(git|hg|svn)$|/node_modules/',
            \ 'file': '\v\.(exe|so|dll)$',
            \ 'link': 'some_bad_symbolic_links',
            \ }
let g:ctrlp_dotfiles = 0
j
"autocmd BufWritePre * :normal gg=G
let g:UltiSnipsExpandTrigger="<c-j>"
let g:UltiSnipsJumpForwardTrigger="<c-b>"
let g:UltiSnipsJumpBackwardTrigger="<c-z>"
let g:UltiSnipsNoPythoWarning = 1

" Syntastic
set statusline+=%#warningmsg#
set statusline+=%{SyntasticStatuslineFlag()}
set statusline+=%*

let g:syntastic_always_populate_loc_list = 1
let g:syntastic_auto_loc_list = 1
let g:syntastic_check_on_open = 1
let g:syntastic_check_on_wq = 0

" C tags
nmap <F8> :TagbarToggle<CR>
nnoremap <Leader>. :CtrlPTag<CR>
inoremap <leader>; <C-o>A;
nnoremap <leader>; A;

set diffopt+=vertical
inoremap <BS> <Nop>
"inoremap <Del> <Nop>

Answer 1

I could reproduce your issue by starting Vim without nocompatible set.

vim -u NONE -U NONE

It seems that the inoremap is not in Vi, so it won't do the map if you don't add the nocompatible option.

e.g. it works with:

vim -u NONE -U NONE -N

Also, as a general rule, you may want to start your vimrc with

set nocompatible

Note: next time have a look at How do I debug my vimrc file?