March 2017 - last edited March 2017
Don't mean to bump this thread, but I use a Mac and thought it'd be helpful to mention what solved this issue for myself. Since I don't have IE, I instead deleted browser history on Safari. I don't know if that solved my problem because I went to Chrome -the browser I currently use- and reset the settings and cleared its history. One of those worked, but I am assuming it was resetting everything in Chrome because I had cleared my browser data to no avail earlier. I didn't like having to do that, but that might've helped.
The incorrect password error occurred on my PC too, so I'm hoping I don't have to go digging for solutions a second time. (unless it gives me this error again here on my Mac)
*sigh* I am having this problem. I just spent the past hour trying everything suggested in this entire thread. I bought a few things from the Store and those downloaded fine... then a little while later I went into my purchase history to download Dragon Valley and all of a sudden I can't log into the launcher. This is insanely frustrating. >:-(