Can't access WP Backend/Admin

[jnewco81]

I have a new problem on a site that i'm managing for a client. The site worked fine a few months back, but all of a sudden I can't access the backend of the site.

WP Admin returns a blank page.

wp-login.php has an error message saying: ERROR: Cookies are blocked due to unexpected output.

I've tried using the Debug function in the config file which gives me some further info:

Warning: Cannot modify header information - headers already sent by (output started at /home/content/n3pnexwpnas01_data03/53/3762453/html/wp-config.php:1) in /home/content/n3pnexwpnas01_data03/53/3762453/html/wp-login.php on line 423

Warning: Cannot modify header information - headers already sent by (output started at /home/content/n3pnexwpnas01_data03/53/3762453/html/wp-config.php:1) in /home/content/n3pnexwpnas01_data03/53/3762453/html/wp-login.php on line 436

I've been looking at that file, but PHP isn't really my thing and I just can't see what the problem is. Presumably it's on line 1!

I'm very puzzled as to why I can't access the backend when the (working) site has been left alone for months.

[mhason · Accepted solution]

Sounds like a plugin conflict. Did you or your client installed a new plugin since the last successful login, or updated any existing plugin?

If you did, disable the plugin through FTP and see if it resolves the issue.