Help! What Is HTTP authentication()?

I have the Windows XP Professional in my machine.
Starting two days ago, whenever I run my application, I get a "Connect to localhost" applet prompted to my screen:
The applet says:
EBasic Authentication Area
and asks User name and Password.
I do not know which User name/Password to fill out. I tried all pairs of username/password that I have ever used, none of them works. When I went ahead to click on the Cancel button in the applet, I got

HTTP Status 401
type: Status report
description: This request requires HTTP authentication().

I know that my application has nothing to do with this problem.
Has anybody encountered the similar situation? And what to do? Please help.

it is usually browser settings that cause authentication error.
Not positive that this would work, but you may try to do this.
tools, internet options, advanced tab, scroll to bottom.
Look for Enable Integrated Windows Auth. (Req. Restart)
uncheck it if it is checked.
Not positive that it would work...
Eric

Thank you, Eric. It still does not work after I tried your suggestion. Anybody has an idea about what is going on?

i would try running a virus scanner maybe? i have win98 and on more than one occasion ive had an alert pop up for every page asking for administrator password or something, but it was a password of mine. still dont know what did that.

I ran this application more than two days ago, and the aforementioned problem did not occur. All I can think of is that I installed the Apache James, which provides a mail server and the name of the server is 'localhost', in my machine about two days ago.
I very much doubt the problem is caused by the James because I have tried to put the James in the recycle bin to see if the problem goes away. It does not.

Randall, how to find out the User Name and password of the localhost? I am working on my machine at home; therefore, the administrator is me.
I have tried all username/password combination that I have ever used and cannot get rid of the pop up. Is there anyway to know the username and password of my own machine?

JiaPei,
i wish i could help. i just noticed that your problem seems similar to what i experienced in that it occurred for no reason. i remember more specifically now my problem was the content advisor saying i couldnt view the page, and i suspect maybe my prob was caused by a trojan or something changing my settings. i believe i had to change my settings back. like i said i have win98 which is quite different. i just got lucky that the password it wanted was one i knew. i do not see a user name and password in the Apache httpd.conf file. i hope someone can help you. perhaps if you try another forum that is specifically about windows XP. check out this site http://www.tek-tips.com