Assistance with Drupal Rebuild permissions issue.

I have recently updated a Drupal 6 site to Drupal 7. All is working well except after installing the content access module I get a notification that I need to rebuild permissions. When I try to do so I get the following error. An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /batch?id=5595&op=do StatusText: Service unavailable (with message) ResponseText: One thing to note is that if the blocks module is disabled the notification that I need to rebuild permissions does not appear. Although I am still unable to rebuild the permissions from the status reports page. I have also tried the following with no success - increasing php memory limit (1024MB) - Deleted all nodes & content types then running the rebuild permissions - no success - Deactivated all modules exept for access control and tried rebuilidng permissions - no success I did notice after deleted all nodes and content type there appears to be 2 nodes left in the database unassigned to a content type ( I recorded the node id's). I can't seem to delete those and for some reason I can't run php filter to use the node node_delete(); function. Not sure if it's related but something to point out. I need assistance resolving this issue. I can provide you with a file and database dump of the site or give you cpanel access to the development server backup. You can do what you like on the backup server we have it running else where. Once you have resolved the issue you will need to provide instructions on how correct the issue so we can roll the changes out on the official dev site.