"MUcomplete
let g:mucomplete#enable_auto_at_startup = 1
let g:mucomplete#completion_delay = 100
let g:mucomplete#can_complete = {}
let g:mucomplete#can_complete.go = { 'omni': { t -> t =~# '\m\k\%(\k\|\.\)$' } }
That doesn't look like a MUcomplete issue. I suggest that you remove MUcomplete, restart Vim and try to complete text with CTRL-X CTRL-O. If you still get errors, you need to fix your omni-completion plugin first.
my vim conf: