Table i18n_strings already exists. in DatabaseSchema->createTable()

When trying to enable i18n_strings after upgrading from D6, I've got the following message:
Table i18n_strings already exists. in DatabaseSchema->createTable()

The Schema in D6 was clean.
The schema in D7 has then the following mismatches (using the very useful Schema module):
textgroup: not in database
context: not in database
column format - differences on: type, not null, length, default
declared: array('description' => 'TODO: please describe this field!', 'type' => 'varchar', 'length' => 255, 'not null' => FALSE)
actual: array('description' => 'TODO: please describe this field!', 'type' => 'int', 'not null' => TRUE, 'default' => 0)
indexes group_context: missing in database

I know how to repair that manually with phpmyadmin. But perhaps there is some not only structure modifications in the table. Perhaps there are some data modifications. For that reason I don't go further waiting some more precise explanation about that.