Apparently, there's nothing we can do about it. It's a Chrome issue.

Fango

I've been using chrome for years and this is the only site I've ever had any issues with. Chrome is the biggest browser in the world with nearly double the market share of the next closest browser: http://www.w3counter.com/globalstats.php . This is a huge issue.

Just saying that its chrome's fault and there is nothing you can do is absurd. The reality is it's a vBulletin issue caused by a bug in chrome, they are too incompetent to find a workaround, and you have no control over your own software.

I've got a couple possible workarounds. When I get a chance, I might PM the mods a fuller explanation, but here's what people can do right now:

"TL;DR" For users:
There are two possible workarounds:
1. go into your settings and turn off Javascript for OCC before you log in, and turn it back on afterward. The error is in a script that isn't needed. Note that turning scripts off is generally a bad idea, and can cause all sorts of other problems, so I don't suggest that you just turn scripts off and leave them off.
2. Only for people who know how to use Chrome Dev Tools: "Inspect element", then find and delete this element: <input type="hidden" name="vb_login_password"> before logging in.

"TL;DR" For OCC:
If you can edit the vBulletin HTML code at all, I think you can work around the issue by removing the *hidden* "vb_login_password" field from the template. It doesn't appear to serve any useful purpose (though it MIGHT be used in another part of the code I don't know anything about), and when I remove it from the page (using the Inspect Element tools), I'm able to successfully log in with Chrome.

My educated guess is that vBulletin was relying on unspecified functionality in a feature that was designed for the way browsers worked 10+ years ago. The code that breaks Chrome is broken in FF and IE11 as well, but in those other browsers, it fails in a different way (doing nothing) that doesn't interfere with the server-side login code.

Another option for OCC would be to simply remove or rename the file clientscript/vbulletin_md5.js. That's where the problem is. Removing the file would cause people's browsers to have Javascript errors, but I think they'd be able to get in. Like almost all systems made in the 2000's, vBulletin is built with workarounds in case Javascript doesn't do exactly what it expects.

What a brilliant comprehensive answer. I can't say I understood much of it but I understood that you understand the issue and have provided a workaround. Thank you just isn't enough.

Yes, thank you very much for providing this solution, schlubby. Hopefully it works for everyone having this problem.

Fango

This worked for me; very nice. My earlier post looks pretty b*tchy in comparison to your civil and knowledgeable breakdown. But that won't stop me from saying I find it rather humorous there is such an easy fix while a large portion of users are turned away and chrome is scapegoated.

thanks for solution

still can not login via chrome.....

The site itself isn't updated, but you should be able to get in with a couple extra steps:
If you're not in Incognito Mode, you should be able to just log in once with this trick and stay logged in indefinitely. If you do depend on Incognito Mode, you might want to try a different browser for a while. I don't think it's technically a Chrome bug, but Chrome updates itself all the time (it's up to Version 35 right now), so it's a bit of a moving target for web developers to shoot for. That might be why it seemed like the issue was fixed for a month or two, but it came back. It's extremely unusual to see Chrome's automatic updates causing problems like this, though, which is why I'd bet that the affected login code in vBulletin isn't standards-compliant, but just always sort of worked till now. That is an extremely common thing in web development.