I am trying to compile a library linking to the version of Botan from the Qt Creator sources with MSVC 2008 but am receiving the following error. MinGW compiles and links it fine. What is the issue?

databasecrypto.obj:-1: error: LNK2019: unresolved external symbol "public: static unsigned int const Botan::Pipe::DEFAULT_MESSAGE" (?DEFAULT_MESSAGE@Pipe@Botan@@2IB) referenced in function "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl DatabaseCrypto::b64_encode(class Botan::SecureVector<unsigned char> const &)" (?b64_encode@DatabaseCrypto@@CA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@ABV?$SecureVector@E@Botan@@@Z)

/*!
    Encodes the Botan byte array \a in as a base 64 string.

    \param in The Botan byte array to encode.
 */
std::string DatabaseCrypto::b64_encode(const SecureVector<Botan::byte> &in)
{
    Pipe pipe(new Base64_Encoder);
    pipe.process_msg(in);
    return pipe.read_all_as_string(); // <-- default parameter here is Botan::Pipe::DEFAULT_MESSAGE
}