Syncronize Users gives Unrecoverable Error

After deleting, reinitializing db and deleting and reloading 1.8 and 1.7, syncronize users gives this error:

Synchronize Users-to-Contacts

unrecoverable error
Sorry. A non-recoverable error has occurred.

Return to CiviCRM menu.

Error Details:

Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -1
[message] => DB Error: unknown error
[mode] => 16
[debug_info] => INSERT INTO civicrm_log (entity_table , entity_id , modified_id , modified_date ) VALUES ('civicrm_contact' , 2 , 102 , 20070816223954 ) [nativecode=1452 ** Cannot add or update a child row: a foreign key constraint fails (`asmcivicrm/civicrm_log`, CONSTRAINT `FK_civicrm_log_modified_id` FOREIGN KEY (`modified_id`) REFERENCES `civicrm_contact` (`id`))]
[type] => DB_Error
[user_info] => INSERT INTO civicrm_log (entity_table , entity_id , modified_id , modified_date ) VALUES ('civicrm_contact' , 2 , 102 , 20070816223954 ) [nativecode=1452 ** Cannot add or update a child row: a foreign key constraint fails (`asmcivicrm/civicrm_log`, CONSTRAINT `FK_civicrm_log_modified_id` FOREIGN KEY (`modified_id`) REFERENCES `civicrm_contact` (`id`))]
[to_string] => [db_error: message="DB Error: unknown error" code=-1 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_log (entity_table , entity_id , modified_id , modified_date ) VALUES ('civicrm_contact' , 2 , 102 , 20070816223954 ) [nativecode=1452 ** Cannot add or update a child row: a foreign key constraint fails (`asmcivicrm/civicrm_log`, CONSTRAINT `FK_civicrm_log_modified_id` FOREIGN KEY (`modified_id`) REFERENCES `civicrm_contact` (`id`))]"]
)

I had messed up my initial install, which had worked properly, and clumsily dropped all the tables from the db – without first unchecking the module, by the way. Then deleted the CiviCRM module files, then deleted the module's entry from the system table of Drupal. Reuploaded the files (this time version 1.8, where 1.7 was previously installed.) Then reinitialized database. At which point, the synchronize command first generated this kind of error. Then, seeing other things not work, either, repeated removal steps above except for the system table modification but with disabling the module first. Then uploaded 1.7 again and reinitialized the db. Now getting the error above.

Noticed another issue similar to this one, close because it couldn't be verified. Am using Drupal 5, PHP 5, MySQL 5.