String data, right truncated during d7 upgrade

when I try to upgrade to d7, I get following error because in the system table for column 'type' the data is too long (javascript library) and the VARCHAR(12) can't get this value.

system module
Failed: PDOException: SQLSTATE[22001]: String data, right truncated: 1406 Data too long for column 'type' at row 229: ALTER TABLE {system} CHANGE `type` `type` VARCHAR(12) NOT NULL DEFAULT ''; Array ( ) in db_change_field() (line 2985 of /includes/database/database.inc).

deleting the rows or shortening the value, the upgrade went well
any help to fix the issue?