Internet Explorer:
http://support.microsoft.com/kb/283185
Firefox:
http://support.mozilla.com/en-US/kb/Cookies
http://support.mozilla.com/en-US/kb/Cannot+log+in+to+websites
Google Chrome:
http://www.google.com/support/chrome/bin/answer.py?hl=en&answer=95647
Safari:
http://docs.info.apple.com/article.html?path=Safari/3.0/en/9277.html
How to edit cookies settings:
Internet Explorer 6
These solutions only apply to Internet Explorer running on Windows.
Cookies
If you are using Internet Explorer on Windows, follow these steps to re-establish the original cookie settings:
1. Start Internet Explorer
2. Click the Tools menu
3. Select Internet Options
4. Select the Security tab
5. Click on the "Internet" content zone, represented by the blue/green planet icon
6. Click the "Default Level" button to set the security level to "Medium"
7. Select the Privacy tab
8. Click on the "Default" button to set the privacy slider to "Medium"
9. Click OK
Once you've done all that, quit and restart Internet Explorer and logging in. If the problem persists and you can't get in, try the next possible solution below.
Clear Temporary Files & History
Another potential solution to the problem described in the question above is to clear the temporary files and history kept by Internet Explorer:
4. Select the General tab
5. Under Temporary Internet Files click "Delete Cookies" and "Delete Files" to remove all stored cookies and temporary files.
6. Click "Clear History" to remove the cached URLs from your browsing history
7. Click OK
Now quit and restart Internet Explorer and try your original target website again. If the problem persists, continue to the next solution.
Date & Time
If your computer's clock is off, it can sometimes cause problems like the one described in the question above. Use Windows' "Date/Time" control panel to make sure your clock is set to the correct date, time, time zone, and daylight savings status. You can use the UW Home Page or the time.gov website to determine the current local time. Once your computer's clock is set correctly, restart Internet Explorer and try your original target website again. If the problem still persists, continue to the next possible solution.
From Microsoft’s Internet Explorer Help Site
Internet Explorer 6 implements advanced cookie filtering based on the Platform for Privacy Preferences (P3P) specification. The P3P specification, developed by the World Wide Web Consortium (W3C), enables you to express your privacy preferences while helping Web sites in clearly describing, in a computer-readable format, how they will use your data
Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.Internet Explorer 6 will notify you of Web sites that do not satisfy your privacy settings. This article describes how to manage your privacy (or cookie) settings in Internet Explorer 6. For information about the default privacy settings in Internet Explorer 6, please see the following article in the Microsoft Knowledge Base:
You can configure your privacy settings in Internet Explorer 6 by clicking Internet Options on the Tools menu, and then clicking the Privacy tab. These settings replace the cookies settings on the Security tab in Internet Explorer 4 and 5 (and the Advanced tab in Internet Explorer 3). The Privacy settings slider has six settings: Block All Cookies, High, Medium High, Medium (default level), Low, and Accept All Cookies. The following Privacy settings are available with the slider:
NOTE: Changing your privacy preferences does not affect the cookie acceptance policy for cookies that have already been set unless you move the slider to Accept All Cookies or Block All Cookies.
Firefox
If you find that you cannot log in to a website that requires a username and password, follow the steps described in this article.
Clearing Cookies:
Cookie settings in Firefox are managed in the OptionsPreferences window's Privacy panel. See OptionsPreferences window - Privacy Panel for information on these settings.
Cookies are enabled by default in Firefox. To check your settings:
3.5/3.6:
· If you are troubleshooting problems with cookies, make sure Accept third party cookies is also check marked. For more information, see Disabling third party cookies.
5. Choose how long cookies are allowed to be stored:
· Keep until: they expire: Each cookie will be removed when it reaches its expiration date, which is set by the site that sent the cookie.
· Keep until: I close Firefox: The cookies that are stored on your computer will be removed when Firefox is closed.
· Keep until: ask me every time: Displays an alert every time a website tries to send a cookie, and asks you whether or not you want to store it.
Clear history for that site
The cookies and temporary data already stored on your computer may be causing the problem. Delete them, then test for your problem:
Clear all cookies and the cache
If deleting cookies for the site with the problem did not fix the error, clear all the cookies stored on your computer and clear the Firefox cache:
Check Extensions and Plugins
Some extensions can cause problems with logging in to websites, especially extensions associated with certain websites. For example:
Some plugins can also cause problems logging in to websites. See the Troubleshooting plugins article for instructions on how to determine whether a plugin is causing your problem.
Remove corrupt cookies file
If you cannot log in to websites after removing the cookies associated with it, clearing your Firefox cache, and trying with your extensions and plugins disabled, and have checked security software, you may have a corrupt cookies file in your Firefox profile folder.
This will remove all your stored cookies and essentially log you out of all saved sessions on all websites.
Chrome
1. Click the Tools menu.
2. Select Options.
3. Click the Under the Hood tab.
4. Click Content settings in the "Privacy" section.
5. Allow Cookies: Make sure "Allow local data to be set" is selected to allow both first-party and third-party cookies. For any given webpage, first-party cookies are cookies that are set by the site domain listed in the address bar. Third-party cookies come from other domain sources that have items, such as ads or images, embedded on the page. If you only want to accept first-party cookies, select the "Block all third-party cookies without exception" checkbox.
6. Make exceptions for cookies from specific websites: To specify how cookies should be handled for a few specific websites, click Exceptions.
7. Automatically clear all cookies when you close the browser: Select the "Clear cookies and other site data when I close my browser" checkbox.
To clear all cookies
Safari
1. Choose Safari > Preferences.
2. Click Security.
3. In the Accept Cookies section, choose how you want Safari to handle cookies. Click the Help (question mark) button to see an explanation of the options.
4. If you want to see more information about the cookies stored on your computer, click Show Cookies. The following information is displayed for each cookie:
a. Website that stored the cookie Name Path, or location, on your computer
b. Secure status; cookies marked “secure” are sent over an encrypted connection
c. Expiration date; when it will be removed from your computer
d. Content; normally a string of code
5. If you’ve set Safari to block cookies, you may need to temporarily accept cookies to open a page. Repeat the above steps, selecting Always. When you’re done with the page, turn off cookies again and remove the page’s cookies.
To clear Cookies:
1. From the Safari menu, click Empty Cache.
2. When asked Are you sure you want to empty the cache?, click Empty.
3. From the Safari menu, click Preferences.
4. Click Show Cookies.
5. From the Cookie dialog box, click to choose a cookie, and click Remove.
6. Alternatively, if you want to delete all cookies, click Remove All.
7. Click Done.