In my site I have problem "Invalid POST data" on ajax form very often.
In code I see, what this happend in function that return FALSE in file
function form_get_cache($form_build_id, &$form_state)
$cached = cache_get('form_' . $form_build_id, 'cache_form')
It can return cache in 90% or return FALSE in near 10% of form fillings
I can't simulate and undestand situation whan this function return FALSE. And can't decide problem.
1 lost form = 1 lost client. It very bad for Company and my practic with Drupal.
Where I must look to find solution?!!!