My dnn 7.2.1 site won't allow me to login. It just returns me to whatever page I clicked the login button from. When I click on register to see if a new user can login, I get a message that says 'A critical Error has occurred.
This behavior applies to any browser. It was suggested that it might be the skin, but I can't login to change the skin.

Can anyone tell me what is going on?

Is this a newly installed DNN installation, or an upgrade? If an upgrade, from which version?

It is an upgrade from 7.1.1 to 7.2.1
However, the behavior started with 7.1.1 and worked for quite a while until just a few days ago.

Check to see if this is generating javascript errors. The best way to do this is by viewing the site with Chrome. Hit F12 to open the developer tools, and select the Console tab. You'll see errors logged there. Click the login link and see what happens.

Also, in Host Settings, are you using the local copy of jQuery, or the hosted one? If you are using the hosted version, uncheck that box.

To login, try appending ?ctl=login to the url.

You might also want to open up the database using SQL Server Management Studio. Look in the EventLog table and find the most recent errors. You'll have to copy the error html and paste into an editor to start reading it. Perhaps there will be some clues there.

Nothing in the Event Log except an IP address that makes no sense as it has nothing to do with the site. No error message at all. Is there a way to change the skin from the folders?

If you have a skin that you think is offending, just change the name of its directory in the Skins directory. DNN won't be able to find it, and will use the default skin.

You were right, but it didn't help. Even with the default dnn skin, I can't get to the admin/ host levels.

Ok, I downloaded Firefox and am able to login where I fail with Chrome and IE. I can't learn anything from the Even Viewer log. It just shows that the Super User logged in and the time etc... No error message. I cleared the cache on IE with no results.

Can you change the skin, at least for testing purposes, to Gravity? Does the problem persist with that skin?

Yes, the problem continues with the gravity skin. Do you think upgrading to 7.2.1 may fix something?

It has been a while since I posted here. I continue unable to login to our site. I was able to use firefox, but recently had to replace the hard drive. Now even firefox doesn't allow me to login to the site.

After login page accepts my credentials, I get sent back to the page I clicked the login button from. If I use the wrong credentials, I get a message that says login failed, but nothing when I use the correct credentials.

Am I the only one experiencing this?

Here are some questions that might help provide an answer:

1. Which version of DNN?
2. Can others (on other comptuers) login?
3. When you cannot login, are there any javascript errors? (Use the Firefox developer tools to check.)
4. What is the URL for the site? (If possible, is there a non-admin user whose username and password you could share so that I can test?)
5. Have there been any recent changes to the site?

If you need to hire someone to look into this, you might consider 1800DNN.com, run by our good friend Aderson Oliviera. If you Google around, you will find others offering similar services. I happen to know Aderson, and he's a good guy!

I am using DNN 7.3
It is not a public site. Only admin users can login. After this question, I went to the site on THIS computer which is a different one than used to make the previous post, and I am able to see the control panel. I then went to my laptop (yet another different machine than the previous post) and tried to login and got NO control panel. I made a non admin user since I am fortunate enough on this machine. it is, TestUser and the password is "changeme" no quotes. The url is www.slamjammers.org.
No changes have been made to the site in the past few months.

Because the login works on some computer, but not others, I am tempted to blame the client computers for the problem.

Is javascript enabled? With Chrome, open the developer tools and check the Console for errors during login attempt? Also cookies?