I am using batch process to pass users to an external site using their API.

for each user I set `$batch['operations'][] = array('process_funcion', array(LIST OF VARIABLES));`

The batch processing works for upto 5000 users... anything over that I get 

    Access denied
    You are not authorized to access this page. 

I thought this had to do with max_packet size... but I am not to sure of that anymore.

the batch is being initiated after a form is being processed.

any ideas on how I can process 5000 users at a time or why I am getting this access denied?

Would really appreciate the help :)