Drupal error message: “call_user_func_array() expects parameter 1 to be a valid callback”
After doing a series of updates to a Drupal installation, the following error appeared on all admin pages and edit pages:
“call_user_func_array() expects parameter 1 to be a valid callback, function ‘clients_access_callback “
Other symptoms included that the database could not be updated to complete some of the following updates, and search no longer worked.
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