Regular expression search

[vb]

let's say I need a function to find first printable character on the line 
where the pointer is. This is what I'm trying to use:

(defun vb-first-printable ()
  (interactive)
  (let (limit-position)
    (beginning-of-line)
    (next-line 1)
    (setq limit-position (point))
    (previous-line 1)
    (re-search-forward "\\S" limit-position 't)))

when I try executing this, I get the following error:

====================================================
Debugger entered--Lisp error: (invalid-regexp "Premature end of regular 
expression")
  re-search-forward("\\S" 3543 t)
  (let (limit-position) (beginning-of-line) (next-line 1) (setq limit-position 
(point)) (previous-line 1) (re-search-forward "\\S" limit-position (quote 
t)))
  vb-first-printable()
  call-interactively(vb-first-printable)
===================================================

the same problem happens when I try re-search-forward from the command line: 
if I enter "\S" as the pattern to search, I get "premature end of regular 
expression" error,  but if I enter "\\S" as the regular expression pattern, 
the only thing it finds is this pattern (\\S) itself (as I try it on the same 
file where the source code is).

What am I missing here?

TIA,
\vb