I am having the same problem
I added is_array condition in between, and it's ...

Contribution Date
Technology
Drupal
Contribution Project
Date
Contribution Details

I am having the same problem
I added is_array condition in between, and it's working for me right now

The line 544 now looks like:
if (module_exists('date_repeat') && is_array($form_values[$field_name]) && array_key_exists('rrule', $form_values[$field_name])) {

Contribution Author
Nikunj Kotecha
Contribution Issue Link
warning: array_key_exists() [function.array-key-exists] when creating content with CCK Date fields
Contribution Link
https://www.drupal.org/project/date/issues/442312#comment-2785000
Files count
0
Patches count
0