New Post: VS2012 + W7 + Platform Toolset = XP

We had functional project (C++ dll) developed in Visual Studio 2012 using Casablanca v.1.4. We've upgraded it to v.2.2 (using Visual Studio NuGet Manager - Manage NuGet Packages...). After some tweaks (json related) it was built with no error.
Project has Platform Toolset set to "Visual Studio 2012 - Windows XP (v110_xp)" and this is now causing some unexpected behaviour if we try to create new http_client with http_client_config:

...
http_client_config client_config;
web_proxy wp(szProxy);
client_config.set_proxy(wp);

http_client client(szURL, client_config); //Unhandled exception Microsoft C++ exception: std::length_error at memory location 0x0039DCE0.

If we change Platform Toolset to "Visual Studio 2012 (v110)" everything is fine, but we need it to be built for XP (as was possible with v.1.4). :)

OS: Windows 7 64b
Visual Studio 2012 - Configuration: Debug; Platform: Win32;