Plugin conflict!
If you have both Ultisnips and NeoComplete then you cannot use the same key for expansion. I used to have tab mapped out to both for completion with AutoComplPop and Ultisnips. I had tab set for g:UltiSnipsJumpForwardTrigger but NeoComplete still doesn't like it. So now, that's changed to Control + Tab and things are good again.
let g:UltiSnipsExpandTrigger="<C-CR>"
let g:UltiSnipsJumpForwardTrigger="<C-tab>"
let g:UltiSnipsJumpBackwardTrigger="<s-tab>"
Only wish one NeoComplete OR Ultisnips makers see this and make it work without conflict