It just happened to me again.  I've been working on my DNN site all day.  Now neither Login or Register work.  I will probably have to reinstall for the 4th time in 2 days.

lousaint,

Is it the crazybapa site you are having trouble with?

If so, try this link to Login : http://crazybapa.com/?ctl=login

It appears that your Login Page is set to go to TabId=0 which is not correct.

Once you login in as Host, go to the Host>SQL window and run this Query:

Update Portals Set LoginTabId=null, RegisterTabId=null Where PortalId=0

Thank you, John

I'm going to keep your link handy.  It got me to the login screen.  I pasted the query into the SQL query box and clicked "Execute".  It threw up this message "There is an error in your Query."   I tried it again, got the same error.   This time there was a lot of "jumping" of the screen; then, same error message.  So I logged out.  Tried to log in again, but the LOGIN link didn't work. 

But we're close.  Can you spot the error in your query?  Assuming we get beyond that, have you any idea how that TabId=0 got there?  What might I have done to cause it?  Since posting this ticket, I've summarized all our problems in one post hoping someone will spot some common cause.  In that post, I mention that the LOGIN problem seems to occur when I change skins.