You need to include a header with the declaration of XMLElement (not to mention <string> for the std::string class). Just because the library is linked doesn't mean the compiler won't complain about unrecognized types.
Even when i do include the header it still errors.
Then it's the wrong header.
Oh, and there is no error about an unrecognized type ;-)
Clearly you and I are reading different errors, because the one you posted says exactly that. "expected constructor, destructor, or type conversion" means a recognized type is expected but wasn't provided.
Well then you'll need to be more specific. What compiler, what OS, give us your exact code in a compact form so that we can reconstruct your project. Because from what you posted, the only answer is "include the correct header".