Vim insert mode not allowing editing of existing lines in file, only newly added lines

Question

It used to be that when I went into insert mode on an existing file, I could hit "delete" and that would work. Now I can still delete and modify things that I newly add to a file, but if there is existing stuff there once I open a file, I do not have the ability to delete that. I can only delete and modify new stuff. Out of insert mode however I still have the ability to delete things with the regular dd type commands. My .vimrc is pretty simple, and my only addon is SuperTab.

Here is my .vimrc if that helps:

set tags=./tags,~/kent/src/tags,~/kent/src/lib/tags,~/kent/src/inc/tags,~/kent/src/hg/lib/tags,~/kent/src/hg/inc/tags,~/kent/src/jkOwnLib/tags  
syntax on
filetype indent plugin on
set modeline
au FileType python setlocal tabstop=8 expandtab shiftwidth=4 softtabstop=4
set background=dark
set wildmode=longest,list,full
set wildmenu

And here is the output from vim --version:

VIM - Vi IMproved 7.3 (2010 Aug 15, compiled Feb  8 2012 10:41:54)
Included patches: 1-434
Compiled by John St. John
Normal version without GUI.  Features included (+) or not (-):
-arabic +autocmd -balloon_eval -browse +builtin_terms +byte_offset +cindent 
-clientserver -clipboard +cmdline_compl +cmdline_hist +cmdline_info +comments 
-conceal +cryptv +cscope +cursorbind +cursorshape +dialog_con +diff +digraphs 
-dnd -ebcdic -emacs_tags +eval +ex_extra +extra_search -farsi +file_in_path 
+find_in_path +float +folding -footer +fork() +gettext -hangul_input +iconv 
+insert_expand +jumplist -keymap -langmap +libcall +linebreak +lispindent 
+listcmds +localmap -lua +menu +mksession +modify_fname +mouse -mouseshape 
-mouse_dec -mouse_gpm -mouse_jsbterm -mouse_netterm -mouse_sysmouse 
+mouse_xterm -mouse_urxvt +multi_byte +multi_lang -mzscheme +netbeans_intg 
+path_extra -perl +persistent_undo +postscript +printer -profile +python 
-python3 +quickfix +reltime -rightleft -ruby +scrollbind +signs +smartindent 
-sniff +startuptime +statusline -sun_workshop +syntax +tag_binary 
+tag_old_static -tag_any_white +tcl +terminfo +termresponse +textobjects +title
 -toolbar +user_commands +vertsplit +virtualedit +visual +visualextra +viminfo 
+vreplace +wildignore +wildmenu +windows +writebackup -X11 -xfontset -xim -xsmp
 -xterm_clipboard -xterm_save 
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
      user exrc file: "$HOME/.exrc"
  fall-back for $VIM: "/cluster/home/jstjohn/share/vim"
Compilation: gcc44 -c -I. -Iproto -DHAVE_CONFIG_H     -g -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1     -I/usr/include  -D_REENTRANT=1  -D_THREAD_SAFE=1  -D_LARGEFILE64_SOURCE=1  
Linking: gcc44   -L/usr/local/lib -Wl,--as-needed -o vim       -lm -lncurses -lnsl  -lselinux      -L/hive/groups/recon/local/lib/python2.7/config -lpython2.7 -lpthread -ldl -lutil -lm -Xlinker -export-dynamic  -L/usr/lib -ltcl8.4 -ldl -lpthread -lieee -lm    

Answer 1

You most likely need to set backspace+=start. Generally you probably want set backspace=indent,eol,start, but just "start" should solve this problem specifically.

See :help 'backspace' for more information on the other options.