ERROR: Cookies are blocked due to unexpected output

I had a same problem to both of my managed sites since I noticed them yesterday noon (GMT+8), I also noticed there are quite a few same reports from other users in www.remarpro.com forum.
Before the problem occurred, I just updated the WordPress and changed some setting of certain plugin, however, I tried to renamed the folder of certain plugin by following some tips from users’ advices found online, but it did not work.
Looking forward to solution coming up.

For the record, I just received a warning of hacked from Google console and then I initiated a search for hacker issue associating problem of this thread, and then I found another case quite identical to my case in WordPress forum through Google search, I quote:

A site I run for a client was hacked, and it made everything terrible. I’ve tried unsuccessfully to clean it up, deleting all the files I can find via FTP that don’t belong there. I’ve removed and replaced all the WP core files. But after all of this, I can’t log in. wp-admin brings me to a blank page and wp-login.php brings me ERROR: Cookies are blocked due to unexpected output.

I’m still working on the problem.

I have the same issue, I installed a plugin today and when saving changes directed me to a post.php a blank page, I managed to go back from the blank page and continue working, but it kept happening each time I saved a page.

I thought it was just a cache issue, I uninstalled the plugin just in case. Afterwards trying to login into a different browser got this error message:

ERROR: cookies have been blocked due to an unexpected result. To get help look up this documentation or check the support forums

I have not been able to login and I do have cookies enabled in both browsers.

Have you tried:
– deactivating ALL (yes all) plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s).
– If you can’t get into your admin dashboard, try resetting the plugins folder by FTP.
– switching to the unedited default Theme (Twenty Sixteen, etc.) for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins). If you don’t have access to your admin area, use FTP , or your web-host’s cPanel or whatever file management application your host provides (no Dashboard access required). Navigate to /wp-content/themes/ and switch to the default theme by renaming your current theme’s folder by adding “-old” to the end of the folder name. Alternately, you can remove other themes except the default theme. That will force your site to use it.

If the above trouble shooting steps do not help, then try Enabling debugging and post the results.

Thank you Tara, I did as you said and was able to find the error, it was in a piece of code copied from a forum and pasted into the functions.php of my child theme, a function that was to hide the category of the blog entries in the archive.php template.

It turned out that the code was not working as expected, it was affecting WordPress. I am not a programmer, but with your help is fixed. It was not any issue with plugins.

Thank you again!!!

You are welcome ??

Good day,

I was able to resolve it by doing this.

I had added a code in my functions.php and then this error started.

I removed the code but the error was still there.

I then discovered that there were spaces below the last line in the functions.php (?>)

So I deleted the spaces below ?> and it worked

Hi eoriaifo,

Your solution works for me. Thanks! I think it’s header problem.

Thanks Anyway!

Hola eoriaifo

Thanks so much for letting us know your solution. It worked like a charm