Which version of AWB are you using? It has gone through changes since April that may affect this issue. If you aren't using the current version, you will have to manually download and install it, as Sourceforge made changes that rendered previous versions' updater unusable.

5.8.7.0
This is what the AWB updater loaded on Oct 16, 2016

How do I manually download and install the most current version?

I just downloaded the latest version, which does seem to be 5.8.7.0, but downloaded it directly from sourceforge.net. Same results of the login failed.

The error may be dependent on the version of Mediawiki.
AWB 5.8.8.0 works with version 1.26.2, but it gives an error on login for version 1.27.1.

AWB 5.8.0.0 shows message (for MW 1.27.1):

Operation 'login' ended with result 'NeedToken'.
Xml: '<?xml version="1.0"?><api><warnings><login xml:space="preserve">Fetching a token via action=login is deprecated. Use action=query&meta=tokens&type=login instead.</login></warnings><login result="NeedToken" token="e81b941bf1822445a1fd50582324e2a45818432b+\" /></api>'

Just a note, since I don't understand "The error may be dependent on the version of Mediawiki.". I never get as far as a wiki. The AutoWikiBrowser opens (it's now version 5.8.8.0). It won't let me sign in, so I don't get to run it. No wiki involved. Whatever is wrong, it has nothing to do with any wiki version on my end. ~~~~

In T148342#2807381, @Maile66 wrote:

Just a note, since I don't understand "The error may be dependent on the version of Mediawiki.". I never get as far as a wiki. The AutoWikiBrowser opens (it's now version 5.8.8.0). It won't let me sign in, so I don't get to run it. No wiki involved. Whatever is wrong, it has nothing to do with any wiki version on my end. ~~~~

Well, if you're trying to sign in, that's a week being involved. AWB is just "proxying" the login to the Wiki, you're not logging into AWB

I see. Well, in that case, it must be the English Wikipedia wiki., which says version 1.29.0-wmf.3 (rMWeb7c296a7ad4). I'm always on that, and have never tried to use AWB for anything else. So, it stands to reason that if other English Wikipedia have no trouble with AWB, it's not the wiki.~~~~

In T148342#2807392, @Maile66 wrote:

I see. Well, in that case, it must be the English Wikipedia wiki., which says version 1.29.0-wmf.3 (rMWeb7c296a7ad4). I'm always on that, and have never tried to use AWB for anything else. So, it stands to reason that if other English Wikipedia have no trouble with AWB, it's not the wiki.~~~~

But also that version of AWB is working for a lot of people.... If it wasn't, we'd be getting a lot of complaints.

Do you get a log file created wherever you're running AWB from?

How do I create a log file? I can't run AWB. I can only open the browser. That's as far as it gets, since it won't let me log in. ~~~~

Oh I think she is using the Java version of AWB not the client version.

There's a difference? I just ran the Microsoft compatibility troubleshooter on AWB. It didn't show anything different, and didn't correct the issue. ~~~~

Yes, the AWB script is run through the web using Java scripting and was created and is maintained by Joeytje50. Then there is the client version that is the one that Reedy, RJ and Magioladitis support. It's really confusing and hopefully Joey renames his app so it won't be as confusing.

There may be problems with your password. This error occur also when password is not enough long (after latest MediaWiki updates).
Logging through the web interface of wiki is ok? Try to log out and login again and you may see such a message:

Your password is not valid: Passwords must be at least 8 characters.
Please choose a new password now, or click "Skip" to reset it later.

Please close this ticket. I have uninstalled AWB and will not be going back to it. My password was never an issue, since AWB never let me get as far as trying to enter it. All I did was click on the button to log in, and the error message came up. Too much trouble for too little benefit. Enough. Close the ticket.

In T148342#2815136, @Maile66 wrote:

Please close this ticket. I have uninstalled AWB and will not be going back to it. My password was never an issue, since AWB never let me get as far as trying to enter it. All I did was click on the button to log in, and the error message came up. Too much trouble for too little benefit. Enough. Close the ticket.

Apart from that doesn't make sense. Login can't fail when you haven't tried to login

Well, let me clarify that for you so it makes sense. When I first posted here a month ago, it would let me input the password and then flip up the error message. I had the previous version, was that 5.8.7.0 or 5.7.7.0 (whatever it was)? I upgraded to 5.8.8.0 on Nov 18. After that, it wouldn't even let me input the password. It just flipped up the error that it aborted as soon as I clicked the blank to sign in.

Bottom line...if it doesn't work for me, it doesn't work for me. If nobody can figure out why, then nobody can figure out why. So, I've deleted it off my computer and have no intention of trying to download it again. Thanks for the efforts here, but please close the ticket.

@Reedy this should probably be closed.