Migrating legacy business partner data can be a pain, especially if when then legacy system did not check the address as acurate as C4C does.
In my last project I had to migrate thousands of business partner records, with invalid address data. Mainly invalid postal codes and email addresses made C4C to refuse the migration of affected records. The clean way would be to correct the invlid records and upload only the valid records. But if the deadline is close, there are thousands of records to be corrected and you need to learn the valid postal code formats of around 20 countries, then it might be recommendable to migrate the legacy data as it is. This can save you days of effort.
To switch off the Address Validity Check, do the following:
Navigate to WoC Business Configuration > WCView Implementation Project
Open Activity List
In Fine-Tune add action Address Checks to your project and open it
Check the checkbox "Allow saving of inconsistent addresses"
When the checkbox is checked, invalid addresses will raise warnings instead of errors and the data will be migrated successfully.
Once the migration is completed, you can uncheck the checkbox (enable validity check), so that business users are not allowed to maintain invalid addresses. When a user changes a record that was migrated with an invalid address, she will not be able to save that record unless she corrects the address.
You can keep the checkbox checked as well, to allow business users to maintain invalid addresses.