Operating System: Any.
Background: 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:
To prevent DoS (Denial of Service) attacks.
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: I've seen many possible solutions offered to get around the Error 999 message. Many of the solutions seem rather dubious to me, but I will present them all here:
Suggestion: Clear your browser's cookies and cache (temporary files).
Chances of Working: Low. From what I can tell Yahoo isn't using cookies to remember that you've been blocked, so clearing your cookies should have no effect.
Suggestion: 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/
Chances of Working: Low. Whenever I have tried this I log in ok but then get an error message saying "Unfortunately, there is a server problem preventing access to this page. We are working on this problem, and functionality will be restored as soon as possible. Please try again in 10 minutes." This appears to be a slightly friendlier, but no more useful, version of the Error 999 message.
Suggestion: Use the "secure" option when logging into Yahoo rather than the usual "standard" mode.
Chances of Working: Medium. I have had reports that this can work when trying to get into Yahoo Mail, but I suspect it won't help with Yahoo Groups.
Suggestion: Double or multiple click on the "Sign in" button instead of single click.
Chances of Working: Low. I'm not sure what the rationale is behind this suggestion; maybe to try and confuse Yahoo while you're logging in? In my experience this doesn't work.
Suggestion: If you use a proxy server then try turning it off.
Chances of Working: 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.
Suggestion: 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.
Chances of Working: Good. See previous suggestion for the reasons why this should work. Obviously if you've got a static IP address (i.e. you're using a cable modem) then this won't work.
Suggestion: Access your Yahoo mailbox via http://wap.oa.yahoo.com/
Chances of Working: Good. http://wap.oa.yahoo.com/
is a WAP (Wireless Application Protocol) gateway into Yahoo which allows you to access Yahoo Mail. It's very limited but at least you should be able to view your email. Doesn't help you access Yahoo Groups or other Yahoo services though.
Suggestion: Log into Yahoo Messenger and then try accessing Yahoo.
Chances of Working: Unknown. I don't use Yahoo Messenger so I can't comment.
Suggestion: Use a different browser.
Chances of Working: Medium. I have had a report from someone that said they received the Error 999 message when trying to sign into Yahoo Mail with Internet Explorer. They switched to Firefox and the problem went away. This suggests some sort of cookie problem to me, there shouldn't be any real difference between accessing Yahoo with IE or an alternative browser, other than having different settings within the browsers.
Suggestion: Access Yahoo Mail through an email client such as Outlook Express, Eudora, etc.
Chances of Working: Good. You can pay Yahoo for their Yahoo! Mail Premium service. This allows you to access your Yahoo mailbox through Yahoo's POP3 and SMTP servers. See http://help.yahoo.co...lp/us/mail/pop/
for more info.
Suggestion: If you have a web accelerator then try turning it off.
Chances of Working: Good. I've had a couple of reports from people that said turning off their web accelerators fixed the Yahoo Error 999 problem.
Why might the suggestions above that involve changing your IP address not work for some people? Possibly because your new IP address, which prior to being assigned to you may have been used by someone else that accessed Yahoo a lot, may have already been blocked by Yahoo. It is for this reason that using a proxy server to access Yahoo is a bad idea because many other people may be using the same proxy server to access Yahoo, and Yahoo will attribute all these people's traffic to the proxy server's IP address. In addition, you may actually be using a proxy without knowing it! This is called "transparent caching", where all outgoing HTTP requests are intercepted by a proxy (usually your ISP's proxy) and all responses are cached. This sort of set-up is typically used in large companies, so you may find that you can access Yahoo from home but not from work because other employees have been using Yahoo heavily.
Why might the suggestions above, that I rate as having a low probability of working, work for some people and not others? Possibly because the person inadvertently changed their IP address (i.e. They decided to clear out their cookies so they disconnected from the Internet, cleared out the cookies and then reconnected. Low and behold it worked! They then attribute clearing their cookies to fixing the problem, not realising that by disconnecting from the Internet and then reconnecting they probably received a different IP address).
Official Response From Yahoo:
Someone has reported receiving the following email from Yahoo:
The Error 999 code is a result of pirated IP addresses, and the blockage has been instituted as an Abuse safeguard. In these instances, Yahoo! has intentionally blocked these IP addresses. Yahoo! monitors all network activity and when they notice a significantly high amount of activity coming from a specific IP address or a proxy, Yahoo! blocks it. The downfall to this is that most pirated IP addresses belong to small business or home users. When Yahoo! blocks the IP address to safeguard against getting hit, the original owners of the IP addresses also get blocked.
This fits in with my theory of Yahoo monitoring traffic usage per IP address.