Inexplicable error with std::string

From: Dave (better_cs_now_at_yahoo.com)
Date: 12/31/03 

Date: Wed, 31 Dec 2003 06:32:57 -0700

Can anybody tell me why the code below should produce the error below? I'm
going nuts here! Am I missing something incredibly obvious and simple?

std::string::size_type idx;
std::string one_line;
.
.
.
idx = one_line.find('\t', 0);

error C2059: syntax error : 'constant'