Relocation error when linking extension

Hi all!

I'm trying to use std::string and nsEmbedString classes in my c++ 
extension module on Mac, but when I run the build I get this error:

ld: /var/tmp//ccPxeloy.o illegal reference for -dynamic code (section 
difference reference from section (__TEXT,__eh_frame) relocation entry 
(154) to symbol: nsACString::Assign(char const*, unsigned int) defined 
in dylib: 
/Users/mozilla/src/mozilla/firefox-release/dist/sdk/bin/libxpcom.dylib)
/usr/bin/libtool: internal link edit command failed.

But when I build without using nsEmbedString everything builds just 
fine. The problem is that I have to convert UTF8 to UTF16 strings to 
fire notifications through nsIObserverService.

What am I doing wrong?

Any help will be greatly appreciated.

Thank you!
Yury Kovalchuk.