The error appears when Contact Form 7 cannot locate a writable temporary folder for uploaded files. It stops the move operation and returns UPLOAD_ERR_NO_TMP_DIR.
PHP relies on the upload_tmp_dir directive or the system default. If the path does not exist or is not readable, the upload fails before validation.
Contact Form 7 also uses wp-content/uploads/wpcf7_uploads or a custom constant. Missing folder or wrong permissions break the process.
Server restrictions such as open_basedir, SELinux, or AppArmor can block access. Disk full or quota exceeded produces the same message.
Conflicting plugins or themes that redefine the temp constant may point to a non‑existent directory. The result is the same error.