What is error 999 when trying to log in for mail at Yahoo

Fixing 999 error is
Wait for few days and check your mail again,or try logging in from http://mail.yahoo.co.uk
OR
http://login.europe.yahoo.com/config/mail?.intl=uk
Some users have had success by using an alternative browser

Error 999 is a sign that Yahoo's defense is in effect.

"This error appears to be a "catch-all" error code that Yahoo serves up when it doesn't have a more specific error code. It essentially means "Oops! Something went wrong but we don't know what, so we'll just say that Error 999 occurred." The most common reason for receiving Yahoo Error 999 is due to some sort of bandwidth limiting system that Yahoo has put in place on their servers. Once you have exceeded your allotted bandwidth for a specific period of time Yahoo gives you this Error 999 message and doesn't allow you to access the service. People have primarily reported receiving this error when they try to access Yahoo Mail or Yahoo Groups, but other Yahoo services may also be affected.
Why has Yahoo done this? There are two reasons that I can think of:

1. To prevent DoS (Denial of Service) attacks.
2. To stop automated tasks from hammering their servers with hundreds of requests a second.

There are many programs around that offer to automate access to various Yahoo services, i.e. check your Yahoo mailbox every 5 minutes, archive Yahoo Groups messages, download files from the Yahoo Groups Photos and Files sections, etc. If you use one of these automated tools then there is a very real possibility that you will run into the Error 999 message. Normal human usage of the Yahoo services shouldn't normally generate enough traffic to trigger the Error 999 message unless you're a very heavy user.
It appears that Yahoo uses your IP address to track the amount of traffic you're generating on Yahoo, and once you reach the limit you get blocked by the Unable to process request at this time -- error 999 message. Once triggered you will find that your IP address has been blocked for a period of time, somewhere between 2 and 24 hours usually
Resolution Steps:Clear your browser's cookies and cache (temporary files).
2.Log into Yahoo through a different country's server. I.e. if you usually log into Yahoo via http://login.yahoo.com/ then try http://login.korea.yahoo.com/ or http://login.europe.yahoo.com/.
If you use a proxy server then try turning it off. Good. Because Yahoo appears to be using your IP address to track your traffic usage, switching off your proxy (or bypassing your ISP's proxy server and accessing the web directly) will result in you accessing Yahoo via a different IP address (i.e. you will be accessing Yahoo via your real IP address and not via the proxy server's IP address). Thus Yahoo will think you're a different person because you're using a different IP address. If you're using a dial-up modem or some other access method that results in you using a dynamic IP address, try disconnecting from the Internet and waiting a few minutes and then reconnecting.

Use a different browser,if you have a web accelerator turn it off
hope this helps

You can access your email here for now until Yahoo gets all the bugsout. They have been upgrading their servers lately, causing problemsfor all of us. http://us.m.yahoo.com/p/mail Or: http://de.m.yahoo.com/p/mail It's basic, but it works. I used it last night when they were messing around with my compose screen.

◘ Error 999 IS a Ban ... a censor tool, used by Yahoo

Help-link:- (( http://www.murraymoffatt.com/software-pr... )

◘ You can do a few things if you are impatient ( re cleanup computer, dump temp files etc) but this will not help error 999 the best option if you have a dynamic IP is to do a full "flick of the switch", and when you power back up you will come back with a new IP, ( with some turn off comp for 8 hours), but usually you get a new IP when you power up straight after the shutdown, you can continue posting the link under the new IP. 

◘ Best quick fix >>>> login to your Yahoo! mail via an international server...http://world.yahoo.com/ and access your mail / ya / 360 /games from there by clicking the mail icon, stay within that browser. That, is the best temp fix for the system

◘ Also reply to Yahoo using the link they give you in that Error 999 page. I did it once or twice and I was free from the Error. It has been said that answering, voting too quickly may cause that Error. So give some gap of 2-3 mins between any two Questions you answer.

◘ Error 999 IS a Ban ... a censor tool, used by Yahoo

Help-link:- (( http://www.murraymoffatt.com/software-pr... )

◘ You can do a few things if you are impatient ( re cleanup computer, dump temp files etc) but this will not help error 999 the best option if you have a dynamic IP is to do a full "flick of the switch", and when you power back up you will come back with a new IP, ( with some turn off comp for 8 hours), but usually you get a new IP when you power up straight after the shutdown, you can continue posting the link under the new IP. 

◘ Best quick fix >>>> login to your Yahoo! mail via an international server...http://world.yahoo.com/ and access your mail / ya / 360 /games from there by clicking the mail icon, stay within that browser. That, is the best temp fix for the system

◘ Also reply to Yahoo using the link they give you in that Error 999 page. I did it once or twice and I was free from the Error. It has been said that answering, voting too quickly may cause that Error. So give some gap of 2-3 mins between any two Questions you answer.

Almost Always I got this problem solved by following the above suggestions

◘ Error 999 IS a Ban ... a censor tool, used by Yahoo

Help-link:- (( http://www.murraymoffatt.com/software-pr... )

◘ You can do a few things if you are impatient ( re cleanup computer, dump temp files etc) but this will not help error 999 the best option if you have a dynamic IP is to do a full "flick of the switch", and when you power back up you will come back with a new IP, ( with some turn off comp for 8 hours), but usually you get a new IP when you power up straight after the shutdown, you can continue posting the link under the new IP. 

◘ Best quick fix >>>> login to your Yahoo! mail via an international server...http://world.yahoo.com/ and access your mail / ya / 360 /games from there by clicking the mail icon, stay within that browser. That, is the best temp fix for the system

◘ Also reply to Yahoo using the link they give you in that Error 999 page. I did it once or twice and I was free from the Error. It has been said that answering, voting too quickly may cause that Error. So give some gap of 2-3 mins between any two Questions you answer.

Almost Always I got this problem solved by following the above suggestions

The most common reason for receiving Yahoo Error 999 is due to some sort of bandwidth limiting system that Yahoo has put in place on their servers. Once you have exceeded your allotted bandwidth for a specific period of time Yahoo gives you this Error 999 message and doesn't allow you to access the service. People have primarily reported receiving this error when they try to access Yahoo Mail or Yahoo Groups, but other Yahoo services may also be affected.
------ source: http://forums.techarena.in/technology-internet/1112227.htm

visit some solus for same.... u might be knowingall these . still have a try
bye]

http://ycoderscookbook.com/tutorials/999_Error.html

Yahoo is still having some problems at the moment. Suggested cures range from Update Adobe Flash Player and Java script to clear IE7 cache, cookies, and browsing history. Different things seem to work for different people. It's causing attachments to not show, 999 errors where it won't let you do a particular action and some people cannot send receive delete or move mail. It's not just Vista either it's happening to some of us on XP. If all else fails go back to classic mail via this link. http://us.mg1.mail.yahoo.com/dc/optout?s... click yes when asked do you want to opt out.