6.x -7.x upgrade path broken - rebuilding permissions fails after enabling Content Access

I'm making upgrade tests from my D6 site to D7 in test environment and I'm having an issue after installing content access module.

Description of the setup and upgrade steps, can be reproduced on my environment

• Upgraded Drupal core from 6.24 to 7.14 without errors
• Migrated all my CCK fields without errors
• Upgraded ACL module (7.x-1.0) + update.php + rebuild permissions, without errors
• Upgraded Content Access module (7.x-1.2-beta1) --> no errors.
• Run update.php after enabling Content Access --> no updates available.
• Rebuilt permissions --> got the error message displayed below.

The error message that I get when rebuilding the permissions after enabling Content Access is as follows:

An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /fi/batch?id=762&op=do StatusText: Service unavailable (with message) ResponseText: PDOException: SQLSTATE[HY000]: General error: 1366 Incorrect integer value: 'author' for column 'gid' at row 1: INSERT INTO {node_access} (nid, realm, gid, grant_view, grant_update, grant_delete) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5), (:db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11), (:db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14, :db_insert_placeholder_15, :db_insert_placeholder_16, :db_insert_placeholder_17), (:db_insert_placeholder_18, :db_insert_placeholder_19, :db_insert_placeholder_20, :db_insert_placeholder_21, :db_insert_placeholder_22, :db_insert_placeholder_23); Array ( [:db_insert_placeholder_0] => 2028 [:db_insert_placeholder_1] => content_access_rid [:db_insert_placeholder_2] => author [:db_insert_placeholder_3] => 0 [:db_insert_placeholder_4] => 1 [:db_insert_placeholder_5] => 0 [:db_insert_placeholder_6] => 2028 [:db_insert_placeholder_7] => content_access_rid [:db_insert_placeholder_8] => 36 [:db_insert_placeholder_9] => 0 [:db_insert_placeholder_10] => 1 [:db_insert_placeholder_11] => 0 [:db_insert_placeholder_12] => 2028 [:db_insert_placeholder_13] => content_access_rid [:db_insert_placeholder_14] => 3 [:db_insert_placeholder_15] => 0 [:db_insert_placeholder_16] => 1 [:db_insert_placeholder_17] => 0 [:db_insert_placeholder_18] => 2028 [:db_insert_placeholder_19] => all [:db_insert_placeholder_20] => 0 [:db_insert_placeholder_21] => 1 [:db_insert_placeholder_22] => 0 [:db_insert_placeholder_23] => 0 ) in node_access_write_grants() (line 3417 of /path/to/modules/node/node.module).

The site in question was originally built on Drupal 5 and upgraded to Drupal 6. The Drupal 6 version of the site works like a charm without any problems. However, I suspect that there is something strange in the access control tables that is causing this problem to occur. The site is rather large and has 46 roles in addition to authenticated / anonymous users. The roles are quite simple, there is one role for each club that have access control rules applied for their own club content etc.

Other ACL modules that are enabled on the D6 site (but not upgraded in my D7-tests yet) include Forum Access and Node Access Node Reference.

Does the error message give any hints about what could be wrong on my ACL tables? What is the record 2028 that occurs in the error message? In theory it is possible (yet requires a lot of coffee) for me to wipe out all access control rules from the D6 site and then re-define the correct permissions to all roles on the D7 site after upgrading if we suspect that there are some ghosts in the ACL tables.

Please give me some suggestions what would be the next steps for troubleshooting this, I'm more than happy to provide my input for the community and help troubleshooting these kind of corner cases.

Markus