Pillar · 24 errors
WordPress & CMS Errors
WordPress powers a huge share of the web, and its most common failures — the white screen of death, database connection errors, plugin conflicts — have well-understood causes and fixes once you know where to look.
WSODWordPress White Screen of Death A blank white page with no error is WordPress’s "white screen of death" — a fatal error with display turned off. critical DB ConnectionError Establishing a Database Connection WordPress can’t reach its database — the whole site goes down with this single line. critical Missing MySQLiYour PHP Installation Appears to Be Missing the MySQL Extension PHP has no working MySQL driver (mysqli) loaded, so WordPress can't connect to the database and the whole site is down. critical Critical ErrorThere Has Been a Critical Error on This Website WordPress's fatal-error protection caught an uncaught PHP error from a plugin, theme, or PHP incompatibility and replaced the page. high Cookies blockedWordPress "Error: Cookies are blocked due to unexpected output" Stray output before the login headers stops WordPress from setting the auth cookie, so login fails. high REST APIWordPress "Updating failed." / "Publishing failed." (Block Editor) The block editor can't get a valid JSON reply from the REST API, so saves and publishes fail. high Capability deniedWordPress "Sorry, you are not allowed to access this page" WordPress denies wp-admin because your user's role/capabilities are missing or the table prefix doesn't match the database. high Memory exhaustedWordPress "Fatal error: Allowed memory size of X bytes exhausted" A plugin, theme, or image task asked for more memory than PHP allows, killing the request with a fatal error. high Drupal WSODDrupal "The website encountered an unexpected error. Please try again later." Drupal's generic fatal-error page that hides the real PHP exception behind a deliberately vague message. high Invalid JSONUpdating Failed: The Response Is Not a Valid JSON Response The block editor's REST API call came back as HTML instead of JSON, so Gutenberg can't save, update, or publish. high rest_forbiddenREST API: Sorry, You Are Not Allowed to Do That (rest_forbidden / 401) Something is blocking authenticated /wp-json/ requests, so the editor, Site Health, and integrations get rejected as unauthorized. high Write to DiskUpload: Failed to Write File to Disk WordPress accepted the file but couldn't save it to wp-content/uploads, almost always a permissions, disk-space, or PHP temp-dir problem. high No ShippingThere are no shipping methods available The customer's address didn't match any shipping zone that has a method attached, so checkout has nothing to offer them. high Upload DirUnable to create directory wp-content/uploads. Is its parent directory writable? WordPress can't write into wp-content/uploads, usually a permissions or ownership problem, occasionally a full disk. high .maintenanceBriefly Unavailable for Scheduled Maintenance An interrupted update left WordPress's hidden . medium HTTP error"HTTP error" Uploading Images to the Media Library A vague "HTTP error" appears mid-upload in the Media Library, usually from PHP memory, the image processor, or a blocked request. medium Nonce failed"Are You Sure You Want to Do This?" (Nonce Error) WordPress blocked an action because the security token (nonce) on the form or link was missing, expired, or invalid. medium Upload blockedWordPress "Sorry, this file type is not permitted for security reasons" WordPress rejects an upload because its extension or sniffed MIME type isn't in the allowed-uploads whitelist. medium Nonce expiredWordPress "The link you followed has expired" WordPress rejects a form POST because it exceeded PHP's upload size limits or the security nonce timed out. medium core_updater.lockWordPress "Another update is currently in progress" A previous core upgrade died mid-run and left a lock row in the database that blocks all further updates. medium Missed scheduleWordPress "Missed schedule" on scheduled posts A scheduled post stays unpublished and shows "Missed schedule" because WP-Cron never fired at the publish time. medium HTTP errorWordPress media library "HTTP error" / "An error occurred in the upload" An image finishes uploading but WordPress fails on the resize step and shows a vague "HTTP error. medium Dest. Folder ExistsInstallation Failed: Destination Folder Already Exists A leftover directory from a failed or interrupted install is blocking WordPress from extracting the new plugin or theme. medium Nonce FailedAre you sure you want to do this? Please try again A WordPress nonce security check failed, so the action was rejected as possibly forged or expired. medium