"Filename cannot be empty in file_unmanaged_save_data()"

Question

We're using Drupal 7.20 and this error message started appearing after trying to add a new context. I removed the context condition, and even restored drush arr from a dump from Friday. All files belong to apache (chown -R apache:apache) and group/owner can do everything (chmod -R 775 * #temporarily).

The message still persists.

Warning: file_put_contents(): Filename cannot be empty in file_unmanaged_save_data() (line 1903 of /var/www/html/includes/file.inc).
The file could not be created.
Warning: file_put_contents(): Filename cannot be empty in file_unmanaged_save_data() (line 1903 of /var/www/html/includes/file.inc).
The file could not be created.
Warning: file_put_contents(): Filename cannot be empty in file_unmanaged_save_data() (line 1903 of /var/www/html/includes/file.inc).
The file could not be created.
Warning: file_put_contents(): Filename cannot be empty in file_unmanaged_save_data() (line 1903 of /var/www/html/includes/file.inc).
The file could not be created.
Warning: file_put_contents(): Filename cannot be empty in file_unmanaged_save_data() (line 1903 of /var/www/html/includes/file.inc).
The file could not be created.
Warning: file_put_contents(): Filename cannot be empty in file_unmanaged_save_data() (line 1903 of /var/www/html/includes/file.inc).
The file could not be created.

Answer 1

Oy! My temp folder had bad permissions.

Of course I only thought of this after I restored a back up from last Friday -- thus, overwriting all the work from this morning and Friday evening. Arg. Okay, Thanks for letting me vent here.

Answer 2

Same symptom (error message), but it was due to exceeded disk quota.