"The dates are invalid." message using drupal_execute (formatting problem?)

I'm using drupal_execute to create an import process for a batch of nodes that contain dates. When I execute the script, I keep getting a "the dates are invalid" message. If I take the dates out of the import script, the node is created just fine, so I'm pretty sure this is related to the date module and how I'm formatting things, but I can't (after multiple days) figure out what I'm doing wrong.

I'm using date 2.4 on a drupal 6.14 install with CCK3 (in order to take advantage of the multigroup module). The date is inside a multigroup, but I get the same error message even when I take the date field out of the group and try importing it that way.

The date field itself is a "date" type (not datetime or datestamp). I'm using a select list widget, but originally I had it as a dropdown calendar (same import results for both widgets). Years backward and forward is set to -10:+10 and granularity is hour/minute/second (though I would prefer just y/m/d).

I was able to look at the $form_state array from a normal node form submission, and the field looks like this:

[field_action_date] => Array
(
[0] => Array
(
[value] => 2006-06-17T00:00:00
[_weight] => 0
[_remove] => 0
[value2] => 2006-06-17T00:00:00
[timezone] => America/Chicago
[offset] => -18000
[offset2] => -18000
)

)

I tried to mimic that format in my code, which looks like this:

$form_state['values']['field_action_date']['0']['value'] = '2006-06-17T00:00:00';
$form_state['values']['field_action_date']['0']['value2'] = '2006-06-17T00:00:00';
$form_state['values']['field_action_date']['0']['_weight'] = 0;
$form_state['values']['field_action_date']['0']['_remove'] = 0;
$form_state['values']['field_action_date']['0']['timezone'] = 'America/Chicago';
$form_state['values']['field_action_date']['0']['offset'] = -18000;
$form_state['values']['field_action_date']['0']['offset2'] = -18000;

Note that above I've hard-coded the values in for testing purposes. I get the same message for hard-coded date values as well as the real date values I'm trying to import, which are formatted the same way. I've also tried alternately assigning just the 'value', both 'value' and 'value2', and finally all the information you see above. Same result every time.

So, I'm pretty sure I'm doing something wrong, I just don't know what it is. I've marked this request critical because a fairly large rollout depends on me getting this to work as soon as possible (I hope that's not seen as rude; I'm just panicked). At this point, I'm willing to try anything, so any ideas would be welcome. If I've missed providing any relevant info, just let me know and I'll post it as quickly as possible.

Thanks!