Unfortunately, WordPress isn't perfect and just like any software program, it has a multitude of problems that can arise out of the blue at any moment. One problem I encountered recently was the inability to login to my blog, rendering it practically useless. I suppose it was a bit like losing the keys to your home leaving you in total limbo.
The error I encountered was a cookie error message via my browser telling me "Cookies are blocked due to unexpected output. For help, please see this documentation or try the support forums."
Okay, it didn't sound like a serious problem at 1st, so I simply cleared my browsing and cookie history, close my browser and reloaded it and tried again.
However, the problem still persisted, so I decided to try several different browsers, but the outcome was the same, I was still getting that damn stupid cookie message.
Next I tried turning off and restarting my Internet router (that's always worth a try) and tried logging in from a different computer. Did it work? Nope, still the same problem.
By now, I determined it was nothing to do with my web browser or computer accepting cookies, but something was seriously wrong with WordPress or my web host.
I was thinking the worst and thought I would have to do a complete fresh install which wasn't something I was experience with, so before I completely panicked I decided to do a Google search on the problem. As usual, Google delivers a mixed bag of results, many of them completely and utterly useless, but after reading multiple websites I determined the problem was something to do with a recent plugin I installed. Not exactly sure which one was causing the problem as I installed several at once, but it is definitely a problem with a WordPress plugin.
Since I couldn't login via my web browser, I had to use an FTP program, such as FileZilla to view and edit my WordPress files on my web hosting server. You can also gain access to these by logging into your web host Control Panel, but for this guide, I'm using FileZilla.
Naturally to login to your web hosting via FileZilla, your gonna need to know your host name, username and password. Once you've logged into your web host, you need to locate your WordPress files. These are usually located in the public_html, but will vary depending on your web host.
Once you've located your WordPress files, the folder we are looking for is named "wp-content". Once you have double clicked on that folder, a new one will open where you will see a folder named "plugins". We don't want to open the plugins folder we just simply want to rename it, which will hopefully then give us access to our WordPress blog.
To rename the plugins using FileZilla simply move your mouse pointer over the folder and right click and select rename. You can call it what you like, as this is just a temporary measure. For example, I simply renamed it to plugins1. Once that is completed do not close FileZilla as you will need it again in a little while.
Okay, the next step is to login (or at least try) to your blog via your web browser, and see if the steps we have just followed has rectified the problem. If you do gain access to your blog, that's great, but you need to alter or remove the offending WordPress plugin, so the problem doesn't arise again.
For that we need to access the plugin option via the WordPress dashboard on the left-hand side. Once you're into your plugin option page, you should notice that none of the plugins are functioning and are displaying an error messages. Or you may even get a message that no plugins are installed. Don't worry, this is completely normal, since we have changed the name of the plugins.
Once the file has been renamed back to its original name, go back to your web browser and your WordPress plugins page and refresh it. If no plugins are being displayed, just keep on refreshing the page until they reappear.
The next and and hopefully final step is to remove the offending plugin or plugins. Ideally, you need to remember what plugin you install or modified before the problem appeared. If you don't know which one is causing the problem, then it's just a case of trial and error, I'm afraid.
You will also notice that all the plugins have now been disabled, so you will naturally need to re-enable them by clicking on the "Activate" button.
If you have regained access to your blog by following this guide, but are still encountering the same problem, despite removing or disabling the plugin you believe is causing the problem, try installing a new WordPress theme. Often some WordPress themes can encounter problems after a WordPress update.
I hope this guide has been useful to you and has solved your problem. It worked for me, but won't necessarily work for everybody. If you are still encountering the "ERROR: Cookies are blocked due to unexpected output" problem, then try posting a message on the WordPress forums where knowledgeable WordPress users will be able to advise you.
As always, make regular backups of your WordPress site because you never know when a serious problem may arise.