This was bothering me for a while now, but I've figured it out.
If you're DotNetNuke based site suffers from the “Impossible Login Phantom” problem which is described as:
“Some of my users can login to the site just fine, but some try to login and nothing happens, they just get back into the login dialog with no feedback of what the problem is. ”
You're in good company. The solution to this is problem is pretty simple: this is a cookie issue. The users need to allow third party cookies. That means that
in IE, go to Tools->Internet options->Privacy tab.
Set the slider to “Low“ if it was higher than that.
That's it. If the slider was already “Low” or lower, I can't help you, but it certainly solved the issue for me.
Now, www.ILDotNet.com can function again. Hope to see you there (If you're from Israel).