I'm not familiar in the least with the module, but isn't it as simple as scraping the page for that error message? Wouldn't you just need to know what div or span it is in and then try to match the particular errors you are looking for?

It's not as if Win32::IE::Mechanize is going to return the message to you like you would get a returned result from a subroutine. It's a bit more involved than that.