Based on the error message it looks like the format of the data is not correct or what is expected from the "last_login".
Without knowing the specific it will be hard to narrow down the exact issue.
I would verify the data in the accounts.last_login field is valid in the auth database. It should be a fine if it is the default from the repack.
Then I would check the CMS page that is generating the error. It may be expecting the value in a different format.
Good Luck