CCK fields not migrating to new fields

I've just successfully updated a Drupal 6 site (6.19) to D7 (Latest dev). The D7 upgrade now works without too many error messages. Content types and vocabularies migrate successfully but all CCK fields do not. They are still there in the database after the migration but it looks like they've not been touched by the update. Their entity names remain the same (content_field_fax for instance).

The CCK fields from D6 do not appear in the listing all of all fields in D7 (or in the D7 content types). I wonder if I am doing something wrong in the upgrade procedure. I disable all contrib modules incl. CCK in CCK, export database and run the update on a fresh D7 install. Initially I thought the missing fields were caused by the use of fieldgroups in D6, but removing the groups didn't make any difference.

Other little errors:

I get this error at the top of every page:
Notice: unserialize(): Error at offset 2 of 3531 bytes in variable_initialize() (line 762 of /var/aegir/drupal7b/includes/bootstrap.inc).